Steps to reproduce:
1. Add a RadMenu to a form
2. Add menu item with two sub menu items
3. Add a mnemonic to the first one e.g. &First
4. Add a shortcut to the second with the mnemonic letter of the first one e.g. Crtl + F
5. Run the application and open the menu popup, press Ctrl + F and you will see that the second item will be clicked and then the first one will be clicked as well.

The reason for this is that RadMenu and the PopupManager are both registered to listen for windows messages. When the popup handles the shortcut the popup receives a message and it handles the mnemonic.