I noticed when you open a RadMenu in design view on a form where you want e.g. add some menu items, and, while the menu is open, you click on another form (e.g. to check on the items you created up there), the menu remains open, even if you navigate through other open windows in VS.
It took me a while to find out which menu I initially clicked on.
Please note, this happens sometimes, I did not find one way I can always reproduce this behavior.
After a few clicks I managed to close the menu...
It is a minor issue.