It happened like 8 times for me while i was playing the Only Throwables mode and Realism Gib Fest (i can't remember more but i know they were all from this mod).

The game instantly minimizes, you can't turn it back on, and somehow you can only use your mouse on the task bar, forcing you to restart your PC. It f*cking sucks, i have no idea how or why does it happen, it stopped happening months and it returned once again to ruin my game.