diff --git a/QMLComponents/boundcontrols/boundcontrolterms.cpp b/QMLComponents/boundcontrols/boundcontrolterms.cpp
index 1e69ef8309..bc6b442e20 100644
--- a/QMLComponents/boundcontrols/boundcontrolterms.cpp
+++ b/QMLComponents/boundcontrols/boundcontrolterms.cpp
@@ -191,8 +191,11 @@ Json::Value BoundControlTerms::makeOption(const Terms& terms, const ListModel::R
 	else if (isSingleRow)
 		optionValue = terms.size() > 0 ? terms[0].asString() : "";
 	else
+	{
+		optionValue = Json::arrayValue;
 		for (const Term& term : terms)
 			optionValue.append(term.asString());
+	}
 
 	result["value"] = optionValue;
 	result["types"] = terms.types();
diff --git a/QMLComponents/components/JASP/Controls/VariablesList.qml b/QMLComponents/components/JASP/Controls/VariablesList.qml
index d22cdc9ecc..10dab4eab5 100644
--- a/QMLComponents/components/JASP/Controls/VariablesList.qml
+++ b/QMLComponents/components/JASP/Controls/VariablesList.qml
@@ -401,7 +401,7 @@ VariablesListBase
 				property bool	containsDragItem:		variablesList.itemContainingDrag === itemRectangle
 				property bool	isVirtual:				(typeof model.type !== "undefined") && model.type.includes("virtual")
 				property bool	isVariable:				(typeof model.type !== "undefined") && model.type.includes("variable")
-				property string	preview:				!isVariable ? "" : model.preview
+				property string	preview:				!isVariable || (typeof model.preview === "undefined") ? "" : model.preview
 				property bool	isLayer:				(typeof model.type !== "undefined") && model.type.includes("layer")
 				property bool	draggable:				variablesList.draggable && model.selectable
 				property string	columnType:				isVariable && (typeof model.columnType !== "undefined") ? model.columnType : ""
diff --git a/QMLComponents/models/listmodel.cpp b/QMLComponents/models/listmodel.cpp
index f681ccc799..f078999b90 100644
--- a/QMLComponents/models/listmodel.cpp
+++ b/QMLComponents/models/listmodel.cpp
@@ -23,6 +23,7 @@
 #include "controls/rowcontrols.h"
 #include "controls/sourceitem.h"
 #include "log.h"
+#include "jsonutilities.h"
 
 ListModel::ListModel(JASPListControl* listView) 
 	: QAbstractTableModel(listView)
@@ -796,8 +797,13 @@ void ListModel::_replaceTerm(int index, const Term &term)
 
 Json::Value ListModel::getVariableTypes(bool onlyChanged) const
 {
-	if (onlyChanged && _listView->hasMandatoryType())
-		return Json::nullValue;
+	return getVariableTypes(_terms, onlyChanged);
+}
+
+Json::Value ListModel::getVariableTypes(const Terms& terms, bool onlyChanged) const
+{
+	if (onlyChanged && _listView->hasMandatoryType()) // Don't need to ask for the changed types: this avoids to add the type in formula when it is not necessary
+		return JsonUtilities::vecToJsonArray(stringvec(terms.size(), columnTypeToString(columnType::unknown)));
 
-	return _terms.types(onlyChanged, this);
+	return terms.types(onlyChanged, this);
 }
diff --git a/QMLComponents/models/listmodel.h b/QMLComponents/models/listmodel.h
index 6c2abadbf1..9854cc1a95 100644
--- a/QMLComponents/models/listmodel.h
+++ b/QMLComponents/models/listmodel.h
@@ -91,6 +91,7 @@ class ListModel : public QAbstractTableModel, public VariableInfoConsumer
 			void					setVariableType(int index, columnType type);
 			columnType				getVariableType(	const QString& name)					const;
 			Json::Value				getVariableTypes(bool onlyChanged = false)					const;
+			Json::Value				getVariableTypes(const Terms& terms, bool onlyChanged = false)	const;
 			columnType				getVariableRealType(const QString& name)					const;
 			QString					getVariablePreview(	const QString& name)					const;
 			QStringList				getUsedTypes()												const;
diff --git a/QMLComponents/rsyntax/formulasource.cpp b/QMLComponents/rsyntax/formulasource.cpp
index 60683a014b..db7b530368 100644
--- a/QMLComponents/rsyntax/formulasource.cpp
+++ b/QMLComponents/rsyntax/formulasource.cpp
@@ -246,7 +246,7 @@ QString FormulaSource::_generateRandomEffectsTerms(const Terms& terms) const
 			result += (hasIntercept ? "1" : "0");
 
 			if (filteredTerms.size() > 0)
-				result += " + " + generateInteractionTerms(filteredTerms, filteredTerms.types(true, componentListModel));
+				result += " + " + generateInteractionTerms(filteredTerms, componentListModel->getVariableTypes(filteredTerms, true));
 
 			result += (hasCorrelation ? " | " : " || ");
 			result += key;
@@ -309,14 +309,14 @@ QString FormulaSource::generateInteractionTerms(const Terms& tterms, const Json:
 }
 
 
-QString FormulaSource::_generateSimpleTerms(const Terms &terms, const Json::Value& changedTypes) const
+QString FormulaSource::_generateSimpleTerms(const Terms &terms, const Json::Value& types) const
 {
 	QString result;
 	int i = 0;
 
 	for (const Term& term : terms)
 	{
-		Json::Value changedType = changedTypes.size() > i ? changedTypes[i] : Json::nullValue;
+		Json::Value changedType = types.size() > i ? types[i] : Json::nullValue;
 		if (i > 0) result += " + ";
 		result += FormulaParser::transformToFormulaTerm(term, changedType, FormulaParser::interactionSeparator);
 		i++;
diff --git a/QMLComponents/rsyntax/formulasource.h b/QMLComponents/rsyntax/formulasource.h
index 05e83fb5c3..605f91cee9 100644
--- a/QMLComponents/rsyntax/formulasource.h
+++ b/QMLComponents/rsyntax/formulasource.h
@@ -82,7 +82,7 @@ class FormulaSource : public QObject
 	void							_addError(const QString& error)																	const;
 	std::string						_controlToOptionName(const QString& name)														const;
 	QString							_generateRandomEffectsTerms(const Terms& terms)													const;
-	QString							_generateSimpleTerms(const Terms& terms, const Json::Value& changedTypes)						const;
+	QString							_generateSimpleTerms(const Terms& terms, const Json::Value& types)								const;
 	std::pair<Terms, Json::Value>	_onlyTrueTerms(const QString& controlName)														const;
 	bool							_areTermsInOptions(ListModelAssignedInterface* model, const Json::Value& options, Terms& terms)	const;
 	void							_addTermsToOptions(ListModelAssignedInterface* model, Json::Value& options, const Terms& terms)	const;