Alt tab doesn't work for me at all in the case of just alt tabbing it doesn't show up anywhere on my desktop or in the tasklist as an app for me to get back in. I then have to go to task manager and end aces high as a task.
HOWEVER, if i launch 'Web Page Help' off the clipgboard/map in the game and that takes me out of the game, I can then alt tab back in normally and AH shows up on the alt tab task manager.
not sure if that helps at all.