diff --git a/Engine/OfxParamInstance.cpp b/Engine/OfxParamInstance.cpp
index 52ee4b557b..628e0a21d7 100644
--- a/Engine/OfxParamInstance.cpp
+++ b/Engine/OfxParamInstance.cpp
@@ -579,14 +579,22 @@ void
 OfxPushButtonInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 void
 OfxPushButtonInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 
@@ -595,21 +603,33 @@ void
 OfxPushButtonInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 void
 OfxPushButtonInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxPushButtonInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -617,14 +637,22 @@ void
 OfxPushButtonInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxPushButtonInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobButton> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -704,7 +732,11 @@ void
 OfxIntegerInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -712,7 +744,11 @@ void
 OfxIntegerInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -720,14 +756,22 @@ void
 OfxIntegerInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxIntegerInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -735,28 +779,44 @@ void
 OfxIntegerInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
 OfxIntegerInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
 }
 
 void
 OfxIntegerInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxIntegerInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -815,8 +875,12 @@ OfxIntegerInstance::setDisplayRange()
     int displayMin = getProperties().getIntProperty(kOfxParamPropDisplayMin);
     int displayMax = getProperties().getIntProperty(kOfxParamPropDisplayMax);
 
-    _knob.lock()->setDisplayMinimum(displayMin);
-    _knob.lock()->setDisplayMaximum(displayMax);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimum(displayMin);
+    knob->setDisplayMaximum(displayMax);
 }
 
 void
@@ -826,8 +890,12 @@ OfxIntegerInstance::setRange()
     int mini = getProperties().getIntProperty(kOfxParamPropMin);
     int maxi = getProperties().getIntProperty(kOfxParamPropMax);
 
-    _knob.lock()->setMinimum(mini);
-    _knob.lock()->setMaximum(maxi);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimum(mini);
+    knob->setMaximum(maxi);
 }
 
 ////////////////////////// OfxDoubleInstance /////////////////////////////////////////////////
@@ -963,21 +1031,33 @@ void
 OfxDoubleInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 void
 OfxDoubleInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
 OfxDoubleInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValueWithoutApplying(_properties.getDoubleProperty(kOfxParamPropDefault, 0), 0);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValueWithoutApplying(_properties.getDoubleProperty(kOfxParamPropDefault, 0), 0);
 }
 
 // callback which should set secret state as appropriate
@@ -985,7 +1065,11 @@ void
 OfxDoubleInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -993,14 +1077,22 @@ void
 OfxDoubleInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxDoubleInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -1008,14 +1100,22 @@ void
 OfxDoubleInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxDoubleInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 void
@@ -1025,8 +1125,12 @@ OfxDoubleInstance::setDisplayRange()
     double displayMin = getProperties().getDoubleProperty(kOfxParamPropDisplayMin);
     double displayMax = getProperties().getDoubleProperty(kOfxParamPropDisplayMax);
 
-    _knob.lock()->setDisplayMinimum(displayMin);
-    _knob.lock()->setDisplayMaximum(displayMax);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimum(displayMin);
+    knob->setDisplayMaximum(displayMax);
 }
 
 void
@@ -1036,8 +1140,12 @@ OfxDoubleInstance::setRange()
     double mini = getProperties().getDoubleProperty(kOfxParamPropMin);
     double maxi = getProperties().getDoubleProperty(kOfxParamPropMax);
 
-    _knob.lock()->setMinimum(mini);
-    _knob.lock()->setMaximum(maxi);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimum(mini);
+    knob->setMaximum(maxi);
 }
 
 KnobPtr
@@ -1161,7 +1269,11 @@ void
 OfxBooleanInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -1169,7 +1281,11 @@ void
 OfxBooleanInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -1177,14 +1293,22 @@ void
 OfxBooleanInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxBooleanInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -1192,28 +1316,44 @@ void
 OfxBooleanInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
 OfxBooleanInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
 }
 
 void
 OfxBooleanInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxBooleanInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -1378,7 +1518,11 @@ void
 OfxChoiceInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 
@@ -1386,7 +1530,11 @@ void
 OfxChoiceInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValueWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), 0);
 }
 
 // callback which should set enabled state as appropriate
@@ -1394,7 +1542,11 @@ void
 OfxChoiceInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -1402,7 +1554,11 @@ void
 OfxChoiceInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -1410,14 +1566,22 @@ void
 OfxChoiceInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxChoiceInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -1425,14 +1589,22 @@ void
 OfxChoiceInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxChoiceInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 void
@@ -1660,7 +1832,11 @@ void
 OfxRGBAInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -1668,7 +1844,11 @@ void
 OfxRGBAInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -1676,14 +1856,22 @@ void
 OfxRGBAInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxRGBAInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -1691,14 +1879,22 @@ void
 OfxRGBAInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxRGBAInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
@@ -1707,14 +1903,22 @@ OfxRGBAInstance::setDefault()
     DYNAMIC_PROPERTY_CHECK();
     double def[4];
     _properties.getDoublePropertyN(kOfxParamPropDefault, def, 4);
-    _knob.lock()->setDefaultValuesWithoutApplying(def[0], def[1], def[2], def[3]);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(def[0], def[1], def[2], def[3]);
 }
 
 void
 OfxRGBAInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 void
@@ -1725,7 +1929,11 @@ OfxRGBAInstance::setDisplayRange()
     std::vector<double> displayMaxs(4);
     _properties.getDoublePropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     _properties.getDoublePropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -1736,7 +1944,11 @@ OfxRGBAInstance::setRange()
     std::vector<double> maxs(4);
     _properties.getDoublePropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getDoublePropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 KnobPtr
@@ -1925,7 +2137,11 @@ void
 OfxRGBInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
@@ -1934,7 +2150,11 @@ OfxRGBInstance::setDefault()
     DYNAMIC_PROPERTY_CHECK();
     double def[3];
     _properties.getDoublePropertyN(kOfxParamPropDefault, def, 3);
-    _knob.lock()->setDefaultValuesWithoutApplying(def[0], def[1], def[2]);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(def[0], def[1], def[2]);
 }
 
 // callback which should set enabled state as appropriate
@@ -1942,7 +2162,11 @@ void
 OfxRGBInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -1950,7 +2174,11 @@ void
 OfxRGBInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -1958,14 +2186,22 @@ void
 OfxRGBInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxRGBInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -1973,14 +2209,22 @@ void
 OfxRGBInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxRGBInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 void
@@ -1991,7 +2235,11 @@ OfxRGBInstance::setDisplayRange()
     std::vector<double> displayMaxs(3);
     _properties.getDoublePropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     _properties.getDoublePropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -2002,7 +2250,11 @@ OfxRGBInstance::setRange()
     std::vector<double> maxs(3);
     _properties.getDoublePropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getDoublePropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 KnobPtr
@@ -2256,7 +2508,11 @@ void
 OfxDouble2DInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
@@ -2265,7 +2521,11 @@ OfxDouble2DInstance::setDefault()
     DYNAMIC_PROPERTY_CHECK();
     double def[2];
     _properties.getDoublePropertyN(kOfxParamPropDefault, def, 2);
-    _knob.lock()->setDefaultValuesWithoutApplying(def[0], def[1]);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(def[0], def[1]);
 }
 
 // callback which should set enabled state as appropriate
@@ -2273,7 +2533,11 @@ void
 OfxDouble2DInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -2281,7 +2545,11 @@ void
 OfxDouble2DInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -2289,14 +2557,22 @@ void
 OfxDouble2DInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxDouble2DInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -2304,14 +2580,22 @@ void
 OfxDouble2DInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
 OfxDouble2DInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 void
@@ -2322,7 +2606,11 @@ OfxDouble2DInstance::setDisplayRange()
     std::vector<double> displayMaxs(2);
     _properties.getDoublePropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     _properties.getDoublePropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -2333,7 +2621,11 @@ OfxDouble2DInstance::setRange()
     std::vector<double> maxs(2);
     _properties.getDoublePropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getDoublePropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 KnobPtr
@@ -2514,7 +2806,11 @@ void
 OfxInteger2DInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -2522,7 +2818,11 @@ void
 OfxInteger2DInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -2530,14 +2830,22 @@ void
 OfxInteger2DInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxInteger2DInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -2545,7 +2853,11 @@ void
 OfxInteger2DInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
@@ -2556,7 +2868,11 @@ OfxInteger2DInstance::setDisplayRange()
     std::vector<int> displayMaxs(2);
     getProperties().getIntPropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     getProperties().getIntPropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -2568,14 +2884,22 @@ OfxInteger2DInstance::setRange()
     std::vector<int> maxs(2);
     _properties.getIntPropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getIntPropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 void
 OfxInteger2DInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
@@ -2584,14 +2908,22 @@ OfxInteger2DInstance::setDefault()
     DYNAMIC_PROPERTY_CHECK();
     int def[2];
     _properties.getIntPropertyN(kOfxParamPropDefault, def, 2);
-    _knob.lock()->setDefaultValuesWithoutApplying(def[0], def[1]);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(def[0], def[1]);
 }
 
 void
 OfxInteger2DInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -2802,14 +3134,22 @@ void
 OfxDouble3DInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
 OfxDouble3DInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValuesWithoutApplying(_properties.getDoubleProperty(kOfxParamPropDefault, 0), _properties.getDoubleProperty(kOfxParamPropDefault, 1), _properties.getDoubleProperty(kOfxParamPropDefault, 2));
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(_properties.getDoubleProperty(kOfxParamPropDefault, 0), _properties.getDoubleProperty(kOfxParamPropDefault, 1), _properties.getDoubleProperty(kOfxParamPropDefault, 2));
 }
 
 // callback which should set enabled state as appropriate
@@ -2817,7 +3157,11 @@ void
 OfxDouble3DInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -2825,7 +3169,11 @@ void
 OfxDouble3DInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -2833,14 +3181,22 @@ void
 OfxDouble3DInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxDouble3DInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -2848,7 +3204,11 @@ void
 OfxDouble3DInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
@@ -2859,7 +3219,11 @@ OfxDouble3DInstance::setDisplayRange()
     std::vector<double> displayMaxs(3);
     _properties.getDoublePropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     _properties.getDoublePropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -2870,14 +3234,22 @@ OfxDouble3DInstance::setRange()
     std::vector<double> maxs(3);
     _properties.getDoublePropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getDoublePropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 void
 OfxDouble3DInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -3038,14 +3410,22 @@ void
 OfxInteger3DInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 void
 OfxInteger3DInstance::setDefault()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setDefaultValuesWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), _properties.getIntProperty(kOfxParamPropDefault, 1), _properties.getIntProperty(kOfxParamPropDefault, 2));
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultValuesWithoutApplying(_properties.getIntProperty(kOfxParamPropDefault, 0), _properties.getIntProperty(kOfxParamPropDefault, 1), _properties.getIntProperty(kOfxParamPropDefault, 2));
 }
 
 // callback which should set enabled state as appropriate
@@ -3053,7 +3433,11 @@ void
 OfxInteger3DInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -3061,7 +3445,11 @@ void
 OfxInteger3DInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -3069,14 +3457,22 @@ void
 OfxInteger3DInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxInteger3DInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -3084,7 +3480,11 @@ void
 OfxInteger3DInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
@@ -3095,7 +3495,11 @@ OfxInteger3DInstance::setDisplayRange()
     std::vector<int> displayMaxs(3);
     getProperties().getIntPropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     getProperties().getIntPropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -3106,14 +3510,22 @@ OfxInteger3DInstance::setRange()
     std::vector<int> maxs(3);
     _properties.getIntPropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getIntPropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 void
 OfxInteger3DInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 KnobPtr
@@ -4130,7 +4542,7 @@ OfxParametricInstance::OfxParametricInstance(const boost::shared_ptr<OfxEffectIn
     }
     for (int i = 0; i < parametricDimension; ++i) {
         const std::string & curveName = getProperties().getStringProperty(kOfxParamPropDimensionLabel, i);
-        _knob.lock()->setDimensionName(i, curveName);
+        knob->setDimensionName(i, curveName);
     }
 }
 
@@ -4144,7 +4556,11 @@ OfxParametricInstance::getCustomOverlayInteractEntryPoint(const OFX::Host::Param
 void
 OfxParametricInstance::onCurvesDefaultInitialized()
 {
-    _knob.lock()->setDefaultCurvesFromCurves();
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setDefaultCurvesFromCurves();
 }
 
 OfxParametricInstance::~OfxParametricInstance()
@@ -4162,7 +4578,11 @@ void
 OfxParametricInstance::setEnabled()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setAllDimensionsEnabled( getEnabled() );
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setAllDimensionsEnabled( getEnabled() );
 }
 
 // callback which should set secret state as appropriate
@@ -4170,7 +4590,11 @@ void
 OfxParametricInstance::setSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setSecret( getSecret() );
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setSecret( getSecret() );
 }
 
 
@@ -4178,14 +4602,22 @@ void
 OfxParametricInstance::setInViewportSecret()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextSecret( getProperties().getIntProperty(kNatronOfxParamPropInViewerContextSecret) );
 }
 
 void
 OfxParametricInstance::setInViewportLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setInViewerContextLabel(QString::fromUtf8(getProperties().getStringProperty(kNatronOfxParamPropInViewerContextLabel).c_str()));
 
 }
 
@@ -4193,7 +4625,11 @@ void
 OfxParametricInstance::setHint()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setHintToolTip(getHint());
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setHintToolTip(getHint());
 }
 
 
@@ -4201,7 +4637,11 @@ void
 OfxParametricInstance::setEvaluateOnChange()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setEvaluateOnChange( getEvaluateOnChange() );
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setEvaluateOnChange( getEvaluateOnChange() );
 }
 
 /// callback which should update label
@@ -4209,7 +4649,11 @@ void
 OfxParametricInstance::setLabel()
 {
     DYNAMIC_PROPERTY_CHECK();
-    _knob.lock()->setLabel( getParamLabel(this) );
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->setLabel( getParamLabel(this) );
 }
 
 void
@@ -4228,7 +4672,7 @@ OfxParametricInstance::setDisplayRange()
     std::vector<double> displayMaxs(dims);
     _properties.getDoublePropertyN(kOfxParamPropDisplayMin, &displayMins[0], displayMins.size());
     _properties.getDoublePropertyN(kOfxParamPropDisplayMax, &displayMaxs[0], displayMaxs.size());
-    _knob.lock()->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
+    knob->setDisplayMinimumsAndMaximums(displayMins, displayMaxs);
 }
 
 void
@@ -4247,7 +4691,7 @@ OfxParametricInstance::setRange()
     std::vector<double> maxs(dims);
     _properties.getDoublePropertyN(kOfxParamPropMin, &mins[0], mins.size());
     _properties.getDoublePropertyN(kOfxParamPropMax, &maxs[0], maxs.size());
-    _knob.lock()->setMinimumsAndMaximums(mins, maxs);
+    knob->setMinimumsAndMaximums(mins, maxs);
 }
 
 
@@ -4257,7 +4701,11 @@ OfxParametricInstance::getValue(int curveIndex,
                                 double parametricPosition,
                                 double *returnValue)
 {
-    StatusEnum stat = _knob.lock()->getValue(curveIndex, parametricPosition, returnValue);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->getValue(curveIndex, parametricPosition, returnValue);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4271,7 +4719,11 @@ OfxParametricInstance::getNControlPoints(int curveIndex,
                                          double /*time*/,
                                          int *returnValue)
 {
-    StatusEnum stat = _knob.lock()->getNControlPoints(curveIndex, returnValue);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->getNControlPoints(curveIndex, returnValue);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4287,7 +4739,11 @@ OfxParametricInstance::getNthControlPoint(int curveIndex,
                                           double *key,
                                           double *value)
 {
-    StatusEnum stat = _knob.lock()->getNthControlPoint(curveIndex, nthCtl, key, value);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->getNthControlPoint(curveIndex, nthCtl, key, value);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4305,7 +4761,11 @@ OfxParametricInstance::setNthControlPoint(int curveIndex,
                                           double value,
                                           bool /*addAnimationKey*/)
 {
-    StatusEnum stat = _knob.lock()->setNthControlPoint(eValueChangedReasonPluginEdited, curveIndex, nthCtl, key, value);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->setNthControlPoint(eValueChangedReasonPluginEdited, curveIndex, nthCtl, key, value);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4331,8 +4791,12 @@ OfxParametricInstance::addControlPoint(int curveIndex,
         return kOfxStatFailed;
     }
 
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
     StatusEnum stat;
-    EffectInstance* effect = dynamic_cast<EffectInstance*>( _knob.lock()->getHolder() );
+    EffectInstance* effect = dynamic_cast<EffectInstance*>( knob->getHolder() );
     KeyframeTypeEnum interpolation = eKeyframeTypeSmooth; // a reasonable default
     // The initial curve for some plugins may be better with a specific interpolation. Unfortunately, the kOfxParametricSuiteV1 doesn't offer different interpolation methods
 #ifdef DEBUG
@@ -4345,7 +4809,7 @@ OfxParametricInstance::addControlPoint(int curveIndex,
             interpolation = eKeyframeTypeCubic;
         }
     }
-    stat = _knob.lock()->addControlPoint(eValueChangedReasonPluginEdited, curveIndex, key, value, interpolation);
+    stat = knob->addControlPoint(eValueChangedReasonPluginEdited, curveIndex, key, value, interpolation);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4358,7 +4822,11 @@ OfxStatus
 OfxParametricInstance::deleteControlPoint(int curveIndex,
                                           int nthCtl)
 {
-    StatusEnum stat = _knob.lock()->deleteControlPoint(eValueChangedReasonPluginEdited, curveIndex, nthCtl);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->deleteControlPoint(eValueChangedReasonPluginEdited, curveIndex, nthCtl);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
@@ -4370,7 +4838,11 @@ OfxParametricInstance::deleteControlPoint(int curveIndex,
 OfxStatus
 OfxParametricInstance::deleteAllControlPoints(int curveIndex)
 {
-    StatusEnum stat = _knob.lock()->deleteAllControlPoints(eValueChangedReasonPluginEdited, curveIndex);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return kOfxStatFailed;
+    }
+    StatusEnum stat = knob->deleteAllControlPoints(eValueChangedReasonPluginEdited, curveIndex);
 
     if (stat == eStatusOK) {
         return kOfxStatOK;
diff --git a/Gui/Gui20.cpp b/Gui/Gui20.cpp
index a47fa8ad86..2508abb648 100644
--- a/Gui/Gui20.cpp
+++ b/Gui/Gui20.cpp
@@ -480,6 +480,9 @@ Gui::removeViewerTab(ViewerTab* tab,
                      bool deleteData)
 {
     assert(tab);
+    if (!tab) {
+        throw std::logic_error("");
+    }
     unregisterTab(tab);
 
     if (tab == _imp->_activeViewer) {
diff --git a/Gui/KnobGuiBool.cpp b/Gui/KnobGuiBool.cpp
index 5bdaf8aace..37108f2569 100644
--- a/Gui/KnobGuiBool.cpp
+++ b/Gui/KnobGuiBool.cpp
@@ -237,7 +237,11 @@ KnobGuiBool::removeSpecificGui()
 void
 KnobGuiBool::updateGUI(int /*dimension*/)
 {
-    _checkBox->setChecked( _knob.lock()->getValue(0) );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    _checkBox->setChecked( knob->getValue(0) );
 }
 
 void
@@ -268,7 +272,11 @@ KnobGuiBool::reflectAnimationLevel(int /*dimension*/,
 void
 KnobGuiBool::onLabelChangedInternal()
 {
-    const std::string& label = _knob.lock()->getLabel();
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    const std::string& label = knob->getLabel();
 
     if ( (label == "R") || (label == "r") || (label == "red") ) {
         QColor color;
@@ -298,13 +306,21 @@ KnobGuiBool::onLabelClicked(bool b)
         return;
     }
     _checkBox->setChecked(b);
-    pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), _knob.lock()->getValue(0), b, 0, false) );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), knob->getValue(0), b, 0, false) );
 }
 
 void
 KnobGuiBool::onCheckBoxStateChanged(bool b)
 {
-    pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), _knob.lock()->getValue(0), b, 0, false) );
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), knob->getValue(0), b, 0, false) );
 }
 
 void
@@ -351,7 +367,11 @@ void
 KnobGuiBool::reflectExpressionState(int /*dimension*/,
                                     bool hasExpr)
 {
-    bool isEnabled = _knob.lock()->isEnabled(0);
+    boost::shared_ptr<KnobBool> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool isEnabled = knob->isEnabled(0);
 
     _checkBox->setAnimation(3);
     _checkBox->setReadOnly(hasExpr || !isEnabled);
@@ -362,7 +382,11 @@ KnobGuiBool::updateToolTip()
 {
     if ( hasToolTip() ) {
         QString tt = toolTip();
-        for (int i = 0; i < _knob.lock()->getDimension(); ++i) {
+        boost::shared_ptr<KnobBool> knob = _knob.lock();
+        if (!knob) {
+            return;
+        }
+        for (int i = 0; i < knob->getDimension(); ++i) {
             _checkBox->setToolTip( tt );
         }
     }
diff --git a/Gui/KnobGuiButton.cpp b/Gui/KnobGuiButton.cpp
index 2f77d837e4..af4222b37c 100644
--- a/Gui/KnobGuiButton.cpp
+++ b/Gui/KnobGuiButton.cpp
@@ -183,7 +183,7 @@ KnobGuiButton::emitValueChanged(bool clicked)
         _button->setDown(clicked);
         _button->setChecked(clicked);
 
-        pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), _knob.lock()->getValue(), clicked, 0, false) );
+        pushUndoCommand( new KnobUndoCommand<bool>(shared_from_this(), k->getValue(), clicked, 0, false) );
     } else {
         k->trigger();
     }
diff --git a/Gui/KnobGuiChoice.cpp b/Gui/KnobGuiChoice.cpp
index 58b9b81e0f..5b91f1eb69 100644
--- a/Gui/KnobGuiChoice.cpp
+++ b/Gui/KnobGuiChoice.cpp
@@ -229,7 +229,11 @@ void
 KnobGuiChoice::createWidget(QHBoxLayout* layout)
 {
     _comboBox = new KnobComboBox( shared_from_this(), 0, layout->parentWidget() );
-    _comboBox->setCascading( _knob.lock()->isCascading() );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    _comboBox->setCascading( knob->isCascading() );
     onEntriesPopulated();
 
     QObject::connect( _comboBox, SIGNAL(currentIndexChanged(int)), this, SLOT(onCurrentIndexChanged(int)) );
@@ -244,7 +248,11 @@ void
 KnobGuiChoice::onCurrentIndexChanged(int i)
 {
     setWarningValue( KnobGui::eKnobWarningChoiceMenuOutOfDate, QString() );
-    pushUndoCommand( new KnobUndoCommand<int>(shared_from_this(), _knob.lock()->getValue(0), i, 0, false, 0) );
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    pushUndoCommand( new KnobUndoCommand<int>(shared_from_this(), knob->getValue(0), i, 0, false, 0) );
 }
 
 void
@@ -367,7 +375,11 @@ KnobGuiChoice::onItemNewSelected()
 
             return;
         }
-        KnobHolder* holder = _knob.lock()->getHolder();
+        boost::shared_ptr<KnobChoice> knob = _knob.lock();
+        if (!knob) {
+            return;
+        }
+        KnobHolder* holder = knob->getHolder();
         assert(holder);
         EffectInstance* effect = dynamic_cast<EffectInstance*>(holder);
         assert(effect);
@@ -385,7 +397,11 @@ KnobGuiChoice::reflectExpressionState(int /*dimension*/,
                                       bool hasExpr)
 {
     _comboBox->setAnimation(3);
-    bool isEnabled = _knob.lock()->isEnabled(0);
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool isEnabled = knob->isEnabled(0);
     _comboBox->setEnabled_natron(!hasExpr && isEnabled);
 }
 
@@ -491,7 +507,11 @@ KnobGuiChoice::getKnob() const
 void
 KnobGuiChoice::reflectModificationsState()
 {
-    bool hasModif = _knob.lock()->hasModifications();
+    boost::shared_ptr<KnobChoice> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool hasModif = knob->hasModifications();
 
     _comboBox->setAltered(!hasModif);
 }
diff --git a/Gui/KnobGuiColor.cpp b/Gui/KnobGuiColor.cpp
index d61fbb55b6..bc312a79ed 100644
--- a/Gui/KnobGuiColor.cpp
+++ b/Gui/KnobGuiColor.cpp
@@ -208,8 +208,12 @@ KnobGuiColor::KnobGuiColor(KnobPtr knob,
     , _colorLabel(0)
     , _colorDialogButton(0)
     , _lastColor( knob->getDimension() )
-    , _useSimplifiedUI( isViewerUIKnob() || _knob.lock()->isSimplified() )
+    , _useSimplifiedUI(true)
 {
+    if (knob) {
+        boost::shared_ptr<KnobColor> k = _knob.lock();
+        _useSimplifiedUI = isViewerUIKnob() || ( k && k->isSimplified() );
+    }
 }
 
 void
@@ -224,7 +228,11 @@ KnobGuiColor::connectKnobSignalSlots()
 void
 KnobGuiColor::getIncrements(std::vector<double>* increments) const
 {
-    int nDims = _knob.lock()->getDimension();
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    int nDims = knob->getDimension();
 
     increments->resize(nDims);
     for (int i = 0; i < nDims; ++i) {
@@ -235,7 +243,11 @@ KnobGuiColor::getIncrements(std::vector<double>* increments) const
 void
 KnobGuiColor::getDecimals(std::vector<int>* decimals) const
 {
-    int nDims = _knob.lock()->getDimension();
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    int nDims = knob->getDimension();
 
     decimals->resize(nDims);
     for (int i = 0; i < nDims; ++i) {
@@ -524,7 +536,11 @@ KnobGuiColor::showColorDialog()
 bool
 KnobGuiColor::isAutoFoldDimensionsEnabled() const
 {
-    return _knob.lock()->getDimension() == 3;
+    boost::shared_ptr<KnobColor> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->getDimension() == 3;
 }
 
 NATRON_NAMESPACE_EXIT;
diff --git a/Gui/KnobGuiFile.cpp b/Gui/KnobGuiFile.cpp
index 3faefdfec5..23c53f9bdd 100644
--- a/Gui/KnobGuiFile.cpp
+++ b/Gui/KnobGuiFile.cpp
@@ -452,7 +452,11 @@ void
 KnobGuiFile::reflectExpressionState(int /*dimension*/,
                                     bool hasExpr)
 {
-    bool isEnabled = _knob.lock()->isEnabled(0);
+    boost::shared_ptr<KnobFile> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool isEnabled = knob->isEnabled(0);
 
     _lineEdit->setAnimation(3);
     _lineEdit->setReadOnly_NoFocusRect(hasExpr || !isEnabled);
@@ -538,7 +542,11 @@ KnobGuiOutputFile::createWidget(QHBoxLayout* layout)
 void
 KnobGuiOutputFile::onButtonClicked()
 {
-    open_file( _knob.lock()->isSequencesDialogEnabled() );
+    boost::shared_ptr<KnobOutputFile> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    open_file( knob->isSequencesDialogEnabled() );
 }
 
 void
@@ -555,9 +563,13 @@ KnobGuiOutputFile::onRewriteClicked()
 void
 KnobGuiOutputFile::open_file(bool openSequence)
 {
+    boost::shared_ptr<KnobOutputFile> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
     std::vector<std::string> filters;
 
-    if ( !_knob.lock()->isOutputImageFile() ) {
+    if ( !knob->isOutputImageFile() ) {
         filters.push_back("*");
     } else {
         appPTR->getSupportedWriterFileFormats(&filters);
@@ -585,7 +597,11 @@ KnobGuiOutputFile::updateLastOpened(const QString &str)
 void
 KnobGuiOutputFile::updateGUI(int /*dimension*/)
 {
-    _lineEdit->setText( QString::fromUtf8( _knob.lock()->getValue().c_str() ) );
+    boost::shared_ptr<KnobOutputFile> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    _lineEdit->setText( QString::fromUtf8( knob->getValue().c_str() ) );
 }
 
 void
@@ -720,7 +736,11 @@ void
 KnobGuiOutputFile::reflectExpressionState(int /*dimension*/,
                                           bool hasExpr)
 {
-    bool isEnabled = _knob.lock()->isEnabled(0);
+    boost::shared_ptr<KnobOutputFile> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool isEnabled = knob->isEnabled(0);
 
     _lineEdit->setAnimation(3);
     _lineEdit->setReadOnly_NoFocusRect(hasExpr || !isEnabled);
@@ -810,7 +830,11 @@ KnobGuiPath::onOpenFileButtonClicked()
         std::string dirPath = dialog.selectedDirectory();
         updateLastOpened( QString::fromUtf8( dirPath.c_str() ) );
 
-        std::string oldValue = _knob.lock()->getValue();
+        boost::shared_ptr<KnobPath> knob = _knob.lock();
+        if (!knob) {
+            return;
+        }
+        std::string oldValue = knob->getValue();
 
         pushUndoCommand( new KnobUndoCommand<std::string>( shared_from_this(), oldValue, dirPath ) );
     }
@@ -974,7 +998,11 @@ KnobGuiPath::_show()
 void
 KnobGuiPath::setEnabled()
 {
-    if ( _knob.lock()->isMultiPath() ) {
+    boost::shared_ptr<KnobPath> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    if ( knob->isMultiPath() ) {
         KnobGuiTable::setEnabled();
     } else {
         bool enabled = getKnob()->isEnabled(0);
@@ -987,7 +1015,11 @@ void
 KnobGuiPath::setReadOnly(bool readOnly,
                          int dimension)
 {
-    if ( _knob.lock()->isMultiPath() ) {
+    boost::shared_ptr<KnobPath> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    if ( knob->isMultiPath() ) {
         KnobGuiTable::setReadOnly(readOnly, dimension);
     } else {
         _lineEdit->setReadOnly_NoFocusRect(readOnly);
@@ -1009,7 +1041,11 @@ KnobGuiPath::getKnob() const
 void
 KnobGuiPath::addRightClickMenuEntries(QMenu* menu)
 {
-    if ( !_knob.lock()->isMultiPath() ) {
+    boost::shared_ptr<KnobPath> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    if ( !knob->isMultiPath() ) {
         QAction* makeAbsoluteAction = new QAction(tr("Make absolute"), menu);
         QObject::connect( makeAbsoluteAction, SIGNAL(triggered()), this, SLOT(onMakeAbsoluteTriggered()) );
         makeAbsoluteAction->setToolTip( tr("Make the file-path absolute if it was previously relative to any project path") );
@@ -1074,7 +1110,11 @@ void
 KnobGuiPath::reflectAnimationLevel(int /*dimension*/,
                                    AnimationLevelEnum /*level*/)
 {
-    if ( !_knob.lock()->isMultiPath() ) {
+    boost::shared_ptr<KnobPath> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    if ( !knob->isMultiPath() ) {
         _lineEdit->setAnimation(0);
     }
 }
@@ -1086,7 +1126,7 @@ KnobGuiPath::reflectExpressionState(int /*dimension*/,
     boost::shared_ptr<KnobPath> knob = _knob.lock();
 
     if ( !knob->isMultiPath() ) {
-        bool isEnabled = _knob.lock()->isEnabled(0);
+        bool isEnabled = knob->isEnabled(0);
         _lineEdit->setAnimation(3);
         _lineEdit->setReadOnly_NoFocusRect(hasExpr || !isEnabled);
         _openFileButton->setEnabled(!hasExpr || isEnabled);
@@ -1098,7 +1138,11 @@ KnobGuiPath::updateToolTip()
 {
     if ( hasToolTip() ) {
         QString tt = toolTip();
-        if ( !_knob.lock()->isMultiPath() ) {
+        boost::shared_ptr<KnobPath> knob = _knob.lock();
+        if (!knob) {
+            return;
+        }
+        if ( !knob->isMultiPath() ) {
             _lineEdit->setToolTip(tt);
         } else {
             KnobGuiTable::updateToolTip();
diff --git a/Gui/KnobGuiGroup.cpp b/Gui/KnobGuiGroup.cpp
index 91f5049cb1..ce70dd7fa2 100644
--- a/Gui/KnobGuiGroup.cpp
+++ b/Gui/KnobGuiGroup.cpp
@@ -146,7 +146,11 @@ KnobGuiGroup::createWidget(QHBoxLayout* layout)
     if ( hasToolTip() ) {
         _button->setToolTip( toolTip() );
     }
-    _checked = _knob.lock()->getValue();
+    boost::shared_ptr<KnobGroup> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    _checked = knob->getValue();
     _button->setFixedSize(NATRON_MEDIUM_BUTTON_SIZE, NATRON_MEDIUM_BUTTON_SIZE);
     _button->setChecked(_checked);
     QObject::connect( _button, SIGNAL(checked(bool)), this, SLOT(onCheckboxChecked(bool)) );
@@ -215,7 +219,11 @@ KnobGuiGroup::eventFilter(QObject */*target*/,
 void
 KnobGuiGroup::updateGUI(int /*dimension*/)
 {
-    bool b = _knob.lock()->getValue(0);
+    boost::shared_ptr<KnobGroup> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool b = knob->getValue(0);
 
     setCheckedInternal(b, false);
     if (_button) {
diff --git a/Gui/KnobGuiParametric.cpp b/Gui/KnobGuiParametric.cpp
index 45fadf2934..95a9f656ed 100644
--- a/Gui/KnobGuiParametric.cpp
+++ b/Gui/KnobGuiParametric.cpp
@@ -184,7 +184,11 @@ KnobGuiParametric::onColorChanged(int dimension)
         return;
     }
     double r, g, b;
-    _knob.lock()->getCurveColor(dimension, &r, &g, &b);
+    boost::shared_ptr<KnobParametric> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    knob->getCurveColor(dimension, &r, &g, &b);
 
     CurveDescriptor& found = _curves[dimension];
     QColor c;
diff --git a/Gui/KnobGuiString.cpp b/Gui/KnobGuiString.cpp
index d3b2e43c07..cbe9b6b2f4 100644
--- a/Gui/KnobGuiString.cpp
+++ b/Gui/KnobGuiString.cpp
@@ -540,7 +540,11 @@ KnobGuiString::onLineChanged()
     if ( !_lineEdit->isEnabled() || _lineEdit->isReadOnly() ) {
         return;
     }
-    std::string oldText = _knob.lock()->getValue(0);
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    std::string oldText = knob->getValue(0);
     std::string newText = _lineEdit->text().toStdString();
 
     if (oldText != newText) {
@@ -585,10 +589,14 @@ KnobGuiString::onTextChanged()
     QString txt = _textEdit->toPlainText();
 
     //txt = stripWhitespaces(txt);
-    if ( _knob.lock()->usesRichText() ) {
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    if ( knob->usesRichText() ) {
         txt = addHtmlTags(txt);
     }
-    pushUndoCommand( new KnobUndoCommand<std::string>( shared_from_this(), _knob.lock()->getValue(0), txt.toStdString() ) );
+    pushUndoCommand( new KnobUndoCommand<std::string>( shared_from_this(), knob->getValue(0), txt.toStdString() ) );
 }
 
 QString
@@ -609,7 +617,11 @@ KnobGuiString::addHtmlTags(QString text) const
     }
 
     ///if the knob had custom data, set them
-    QString knobOldtext = QString::fromUtf8( _knob.lock()->getValue(0).c_str() );
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return text;
+    }
+    QString knobOldtext = QString::fromUtf8( knob->getValue(0).c_str() );
     QString startCustomTag( QString::fromUtf8(NATRON_CUSTOM_HTML_TAG_START) );
     int startCustomData = knobOldtext.indexOf(startCustomTag);
     if (startCustomData != -1) {
@@ -1129,7 +1141,7 @@ KnobGuiString::updateGUI(int /*dimension*/)
         int selectionStart = cursor.selectionStart();
         int selectionEnd = cursor.selectionEnd();
         QString txt = QString::fromUtf8( value.c_str() );
-        if ( _knob.lock()->usesRichText() ) {
+        if ( knob->usesRichText() ) {
             txt = removeAutoAddedHtmlTags(txt);
         }
 
@@ -1267,12 +1279,16 @@ void
 KnobGuiString::setReadOnly(bool readOnly,
                            int /*dimension*/)
 {
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
     if (_textEdit) {
-        if ( !_knob.lock()->isCustomHTMLText() ) {
+        if ( !knob->isCustomHTMLText() ) {
             _textEdit->setReadOnlyNatron(readOnly);
         }
     } else if (_lineEdit) {
-        if ( !_knob.lock()->isCustomKnob() ) {
+        if ( !knob->isCustomKnob() ) {
             _lineEdit->setReadOnly_NoFocusRect(readOnly);
         }
     }
@@ -1298,11 +1314,15 @@ void
 KnobGuiString::reflectExpressionState(int /*dimension*/,
                                       bool hasExpr)
 {
-    bool isEnabled = _knob.lock()->isEnabled(0);
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool isEnabled = knob->isEnabled(0);
 
     if (_textEdit) {
         _textEdit->setAnimation(3);
-        if ( !_knob.lock()->isCustomHTMLText() ) {
+        if ( !knob->isCustomHTMLText() ) {
             _textEdit->setReadOnlyNatron(hasExpr || !isEnabled);
         }
     } else if (_lineEdit) {
@@ -1317,7 +1337,11 @@ KnobGuiString::updateToolTip()
     if ( hasToolTip() ) {
         QString tt = toolTip();
         if (_textEdit) {
-            bool useRichText = _knob.lock()->usesRichText();
+            boost::shared_ptr<KnobString> knob = _knob.lock();
+            if (!knob) {
+                return;
+            }
+            bool useRichText = knob->usesRichText();
             if (useRichText) {
                 tt += tr("This text area supports html encoding. "
                          "Please check <a href=http://qt-project.org/doc/qt-5/richtext-html-subset.html>Qt website</a> for more info.");
@@ -1336,7 +1360,11 @@ KnobGuiString::updateToolTip()
 void
 KnobGuiString::reflectModificationsState()
 {
-    bool hasModif = _knob.lock()->hasModifications();
+    boost::shared_ptr<KnobString> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    bool hasModif = knob->hasModifications();
 
     if (_lineEdit) {
         _lineEdit->setAltered(!hasModif);
diff --git a/Gui/KnobGuiTable.cpp b/Gui/KnobGuiTable.cpp
index 522de17594..0d6e55e521 100644
--- a/Gui/KnobGuiTable.cpp
+++ b/Gui/KnobGuiTable.cpp
@@ -663,7 +663,11 @@ KnobGuiLayers::addNewUserEntry(QStringList& row)
         row.push_back( QString::fromUtf8( comps.getLayerName().c_str() ) );
 
         std::list<std::vector<std::string> > table;
-        _knob.lock()->getTable(&table);
+        boost::shared_ptr<KnobLayers> knob = _knob.lock();
+        if (!knob) {
+            return;
+        }
+        knob->getTable(&table);
         for (std::list<std::vector<std::string> >::iterator it = table.begin(); it != table.end(); ++it) {
             if ( (*it)[0] == comps.getLayerName() ) {
                 Dialogs::errorDialog( tr("Layer").toStdString(), tr("A Layer with the same name already exists").toStdString() );
@@ -711,8 +715,12 @@ KnobGuiLayers::editUserEntry(QStringList& row)
         std::string oldLayerName = row[0].toStdString();
         row[0] = ( QString::fromUtf8( comps.getLayerName().c_str() ) );
 
+        boost::shared_ptr<KnobLayers> knob = _knob.lock();
+        if (!knob) {
+            return false;
+        }
         std::list<std::vector<std::string> > table;
-        _knob.lock()->getTable(&table);
+        knob->getTable(&table);
         for (std::list<std::vector<std::string> >::iterator it = table.begin(); it != table.end(); ++it) {
             if ( ( (*it)[0] == comps.getLayerName() ) && ( (*it)[0] != oldLayerName ) ) {
                 Dialogs::errorDialog( tr("Layer").toStdString(), tr("A Layer with the same name already exists").toStdString() );
diff --git a/Gui/KnobGuiValue.cpp b/Gui/KnobGuiValue.cpp
index dcc787fdd5..db8cb65cba 100644
--- a/Gui/KnobGuiValue.cpp
+++ b/Gui/KnobGuiValue.cpp
@@ -1186,31 +1186,51 @@ KnobGuiDouble::KnobGuiDouble(KnobPtr knob,
 bool
 KnobGuiDouble::isSliderDisabled() const
 {
-    return _knob.lock()->isSliderDisabled();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isSliderDisabled();
 }
 
 bool
 KnobGuiDouble::isAutoFoldDimensionsEnabled() const
 {
-    return _knob.lock()->isAutoFoldDimensionsEnabled();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isAutoFoldDimensionsEnabled();
 }
 
 bool
 KnobGuiDouble::isRectangleType() const
 {
-    return _knob.lock()->isRectangle();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isRectangle();
 }
 
 bool
 KnobGuiDouble::isSpatialType() const
 {
-    return _knob.lock()->getIsSpatial();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->getIsSpatial();
 }
 
 ValueIsNormalizedEnum
 KnobGuiDouble::getNormalizationPolicy(int dimension) const
 {
-    return _knob.lock()->getValueIsNormalized(dimension);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return eValueIsNormalizedNone;
+    }
+    return knob->getValueIsNormalized(dimension);
 }
 
 double
@@ -1218,7 +1238,11 @@ KnobGuiDouble::denormalize(int dimension,
                            double time,
                            double value) const
 {
-    return _knob.lock()->denormalize(dimension, time, value);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return value;
+    }
+    return knob->denormalize(dimension, time, value);
 }
 
 double
@@ -1226,7 +1250,11 @@ KnobGuiDouble::normalize(int dimension,
                          double time,
                          double value) const
 {
-    return _knob.lock()->normalize(dimension, time, value);
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return value;
+    }
+    return knob->normalize(dimension, time, value);
 }
 
 void
@@ -1240,19 +1268,31 @@ KnobGuiDouble::connectKnobSignalSlots()
 void
 KnobGuiDouble::disableSlider()
 {
-    return _knob.lock()->disableSlider();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    return knob->disableSlider();
 }
 
 void
 KnobGuiDouble::getIncrements(std::vector<double>* increments) const
 {
-    *increments = _knob.lock()->getIncrements();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    *increments = knob->getIncrements();
 }
 
 void
 KnobGuiDouble::getDecimals(std::vector<int>* decimals) const
 {
-    *decimals = _knob.lock()->getDecimals();
+    boost::shared_ptr<KnobDouble> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    *decimals = knob->getDecimals();
 }
 
 KnobGuiInt::KnobGuiInt(KnobPtr knob,
@@ -1265,19 +1305,31 @@ KnobGuiInt::KnobGuiInt(KnobPtr knob,
 bool
 KnobGuiInt::isSliderDisabled() const
 {
-    return _knob.lock()->isSliderDisabled();
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isSliderDisabled();
 }
 
 bool
 KnobGuiInt::isAutoFoldDimensionsEnabled() const
 {
-    return _knob.lock()->isAutoFoldDimensionsEnabled();
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isAutoFoldDimensionsEnabled();
 }
 
 bool
 KnobGuiInt::isRectangleType() const
 {
-    return _knob.lock()->isRectangle();
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return false;
+    }
+    return knob->isRectangle();
 }
 
 void
@@ -1290,13 +1342,21 @@ KnobGuiInt::connectKnobSignalSlots()
 void
 KnobGuiInt::disableSlider()
 {
-    return _knob.lock()->disableSlider();
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    return knob->disableSlider();
 }
 
 void
 KnobGuiInt::getIncrements(std::vector<double>* increments) const
 {
-    const std::vector<int>& incr = _knob.lock()->getIncrements();
+    boost::shared_ptr<KnobInt> knob = _knob.lock();
+    if (!knob) {
+        return;
+    }
+    const std::vector<int>& incr = knob->getIncrements();
 
     increments->resize( incr.size() );
     for (std::size_t i = 0; i < incr.size(); ++i) {
diff --git a/Gui/ViewerGL.cpp b/Gui/ViewerGL.cpp
index de5d83cfa4..9d596b9141 100644
--- a/Gui/ViewerGL.cpp
+++ b/Gui/ViewerGL.cpp
@@ -3675,7 +3675,7 @@ ViewerGL::removeGUI()
 {
     // always running in the main thread
     assert( qApp && qApp->thread() == QThread::currentThread() );
-    if ( _imp->viewerTab->getGui() ) {
+    if ( _imp->viewerTab && _imp->viewerTab->getGui() ) {
         _imp->viewerTab->discardInternalNodePointer();
         _imp->viewerTab->getGui()->removeViewerTab(_imp->viewerTab, true, true);
     }