A couple of times when alt+tabbing out of the game and then going into the game again the entire screen sometimes (rarely) goes entirely black. Curiously this sometimes take a second or so before it happens. The game appears to be running normally and the only problem seems to be that absolutely the entire screen is 100% black but if I remember correctly I was still able to play and pause the game even though everything was black.
It can be worked around by alt+tabbing out and into the game a couple more times.