Hi,
Add this line of code after setting the ItemsProvider's ItemsSource property:
comboEditor.ValueType = typeof(int);
By default, the ComboEditorTool's ValueType property is set to typeof(string). In your application, the ComboEditorTool is trying to store the Data.ID int property as a string. This might be causing an issue where the selected value reverts back to null which in turn causes the selected value event to fire twice.