Why can I click on items in the menu bar in Microsoft Office applications and why can I enter text into Microsoft Excel fields after using Alt-Tab to switch to a native Linux application?
This is most likely a bug in certain window managers that do not send applications running in CrossOver a notification that the Alt key has been released when switching windows using Alt-Tab. You can work around the problem by pressing and releasing the Alt key after switching back to the affected Microsoft Office application. Note the problem is not Microsoft Office specific, and could affect any application that changes its behaviour for when the Alt key is held down.