We've already answered to your support ticket, but I'm pasting my answer here as well, so if anyone else have the same problem, they could take a look at this solution.
The problem is not caused by RadContextMenu or RadGridView. It is dedicated to the way you are trying to open the Popup. First of all you say that you want to close RadContextMenu and open the popup. In this case I suggest you to open the popup on RadMenuItem Click. When RadMenuItem is clicked, it will automatically close RadContextMenu. You can also close it manually by setting IsOpen property to false. In your case you are using buttons inside RadMenuItem and they are handling the Click event. So it doesn't reach RadMenuItem and this way RadContextMenu is not closed.
For your other problem - in my opinion there are two ways:
- put TextBox directly as a child of the popup.
- put UserControl as a child of the popup.
Both ways will have similar code. I'm sending you a project how to achieve the desired functionality (I've used UserControl as a child of the popup).
Hopefully this helps.
All the best,
the Telerik team