A NullReferenceException can be thrown when quickly editing different cells with a RadMultiColumnComboBox (placed in the CellEditTemplate of the column) and changing the selection.
System.NullReferenceException HResult=0x80004003 Message=Object reference not set to an instance of an object. Source=Telerik.Windows.Controls.GridView StackTrace: at Telerik.Windows.Controls.MultiColumnComboBox.GridViewDropDownContentManager.OnMouseUp(Object sender, MouseButtonEventArgs args) in Telerik.Windows.Controls.MultiColumnComboBox\GridViewDropDownContentManager.cs:line 283