that’s a nasty one 
The video is self explanatory I think ^^
Had the same today, so I went on an empty server to test it. Found out, that it is also possible to jump onto the roof of that building and glitch out of the map:
Check this thread for the one in Whitechapel
http://forums.warchest.com/showthread.php/40414-Falling-out-of-map-Too-soon-to-report
There’s also one one near the first MG on that map, but it’s only accessible with some walljumps. You can go to the roofs next to the capture point with it, and avoid the halls near the pump.
Yes, that’s right, I almost forgot about that one.
Inside the room, while facing the balcony (with the mounted machine gun) jumping up the wall to your right.