It goes from full screen to windowed mode everytime I alt+tab. It's an easy fix going through the options, but still really annoying.
Weird, but not exactly game breaking. Hard to tell exactly what's causing that.
It's a quirk of all DX10 and DX11 games, BF3 and AC3 will do the same thing.
Doesn't the game support borderless fullscreen windowed out of the box? I think I remember seeing that option in the graphic settings, or around somewhere. If your PC is good enough to maintain 60 FPS all the time, you shouldn't have any framerate problems running the game in BFW mode, and it should solve your Alt+tabbing issues.