Not that other issues can't be in play here, but I get what you describe around 1 in 50 times that I alt tab or use the Windows logo key to switch apps while in full screen mode. Usually I get a TS3 crash a bit later as well, which doesn't really matter since I can't bring the game back up when this happens anyway. After years of putting up with that, I've finally learned to switch to windowed mode first and minimize the TS3 application to the task bar -- it's an annoying extra step going in both directions since I much prefer playing in full screen mode, but have never had problems app switching that way.
