[.804][Crash]Alt-tab CTD - it's back.

The DX Error: Invalid call problem has returned, when Alt-tabbing.  It's not consistently broken for me, and it seems like if I alt tab out and then immediately go back into the game, I'm fine.  But if I spend more time outside the game, like to post a message here, I'll get the error when I try to go back in.  Even then, it doesn't always happen.  But I didn't see this sort of thing at all in .803.