I've prepared a sample out-of-browser application with a RadContextMenu as context menu for a TextBox and a RadContextMenu set as context menu of a RadGridView with an attached behavior.
The user control hosting both the RadGridView and the TextBox is opened on a button click from the main page and everything appears to work as expected.
You can find the application attached. Please take a look and let us know whether it helps achieve the desired. If not, could you please provide more details on your scenario and what you wish to achieve.
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