When RadContextMenu opens we open a additional popup that is used to catch the clicks outside context menu so that we can close it. This is the only possible way of doing it because in Silverlight there is no CaptureMouse(subtree) method.
This is the default behavior and cannot be changed.
One possible solution is to use Popup and to show it manually (e.g. instead RadContextMenu.IsOpen=true, popup.Child = radContextMenu, popup.IsOpen=True) but you will have to manually implement boundary detection and open/close of the popup.
the Telerik team
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