I searched the bug tracker, and i couldn't find this particular glitch and was amazed this hasn't been reported yet. In the Prison/Camo building nearest the ATC tower at North East Airfield. On the top floor, behind the stairs, you can go prone at the right side of the door, crawl forward whilst looking slightly to the left and get inside the glitched room. From here the glitchers are able to shoot out the front side wall, and see surroundings.