Hmm, this is an interesting requirement. We certainly have tooltips that will present itself upon hover. But it sounds like you would like to the the same exclusively using the keyboard.
Have you tried an overlay as well? Seems a bit overkill, but then again, a smartInfo smartTip could be as well. I am just trying to see if the behavior is consistent, or if overlay may fair a bit better here in terms of your requirement of gaining/losing focus. Perhaps it might be the same but worth a shot.