kbswitch: incorrectly placed checkmarks in left-click menu

r67149, VBox 4.3.12.

It's weird and hard to point down the exact way it misbehaves. However, if you select a language from the list, usually a different one will get a checkmark next to it the next time the selection pop-up is opened.

One attempt at repro:

• start kbdswitch from Start menu and reboot ROS (so that it appears in the tray if it didn't before)
• right click the kbdswitch in tray -> Properties -> remove all languages in that list
• add US (default choice), Danish (press D) and Faroese (press F) into that list
• select Danish in kbdswitch -> upper US gets the checkmark
• select the upper US in kbdswitch -> no checkmark at all!