A possible solution is to handle the DropDownOpened
event of RadToolStripItem's DropDownButton. You could access that button by using the OverFlowManager
property of RadToolStripItem which gives you an instance of ToolStripItemsOverFlow class, and then use its DropDownButton
property and subscribe to the DropDownOpened
event of that button.
In the EventHandler you could change the visibility state of the last item, which in our case is the add/remove items menu item, and is a child of the DropDownButton's items collection.
Write back if you need further assistance.
the Telerik team