To reproduce: 1. Add a new form 2. Drag and drop RadApplicationMenu on the form 3. Add RadMenuSeparatorItem at design time 4. Save the form 5. Press Ctrl + Z to undo changes 6. Press Ctrl + Y to redo changes 7. An exception is thrown with message: Object of type 'System.Boolean' cannot be converted to type 'Telerik.WinControls.ElementVisibility'.