Sometimes a little error bubble pops up saying that the nvidia driver version <xyz> has crashed. Doesn't happen everytime though.
I haven't had something like this in any other game. Only happens in arma.
Also it's not like a real alt+tab (which I can do manually and does not crash the game). The game freezes for a random amount of seconds (~1-5s) and then goes into that transparent, "only-the-mouse-is-visible", minimized state.
When I try to tab back in using ESC->Alt+Enter->Alt+Enter the screen stays black for a little while and shows the "Receiving..." message.
More information:
Video settings: http://imgur.com/0O123 (I have played around with most of the settings, except for ATOC, PPA, HDR, Vsync, AspectRatio. Visibility is on 10000 right now but if I play SP missions, I usually set it around 2000-5000)
I have also edited the Nvidia Control Panel and Arma config files like this: http://pastebin.com/CGTr3kii The bug happened before I did that anyways.