diff --git a/PreferencesManager.cs b/PreferencesManager.cs
index c65b5fa..56a2c79 100644
--- a/PreferencesManager.cs
+++ b/PreferencesManager.cs
@@ -315,7 +315,7 @@ private T LoadPrefByScreen<T>(int screenNum, string prefBaseName, string primary
                 // look for the non-screen-specific pref setting, and if found, move it from there.
                 // This is a one-off preferences upgrade.
 
-                if (Screen.AllScreens.Length == 1 || Screen.AllScreens.Length >= screenNum && Screen.AllScreens[screenNum].Primary)
+                if (Screen.AllScreens.Length == 1 || (screenNum < Screen.AllScreens.Length && Screen.AllScreens[screenNum].Primary))
                 {
                     if (reg.GetValueNames().Contains(prefBaseName))
                     {
diff --git a/ScreensaverForm.cs b/ScreensaverForm.cs
index 302520c..4f63bed 100644
--- a/ScreensaverForm.cs
+++ b/ScreensaverForm.cs
@@ -163,14 +163,24 @@ public class GlobalUserEventHandler : IMessageFilter
         private const int WM_KEYDOWN = 0x100;
         private const int WM_KEYUP = 0x101;
 
+        // screensavers and especially multi-window apps can get spurrious WM_MOUSEMOVE events
+        // that don't actually involve any movement (cursor chnages and some mouse driver software
+        // can generate them, for example) - so we record the actual mouse position and compare against it for actual movement.
+        private Point? lastMousePos;
+
         public event UserEvent Event;
 
         public bool PreFilterMessage(ref Message m)
         {
-            if ((m.Msg >= WM_MOUSEMOVE && m.Msg <= WM_MBUTTONDBLCLK)
-                || m.Msg == WM_KEYDOWN
-                || m.Msg == WM_KEYUP)
+            if ((m.Msg == WM_MOUSEMOVE) && (this.lastMousePos == null))
             {
+                this.lastMousePos = Cursor.Position;
+            }
+
+            if (((m.Msg == WM_MOUSEMOVE) && (Cursor.Position != this.lastMousePos))
+                || (m.Msg > WM_MOUSEMOVE && m.Msg <= WM_MBUTTONDBLCLK) || m.Msg == WM_KEYDOWN || m.Msg == WM_KEYUP)
+            {
+
                 if (Event != null)
                 {
                     Event();