As above, when pressing "V" when facing a door the game allows you to pass straight through it.
- Legacy ID
Face a closed door.
Press "V" to vault through the door.
Not only when facing a door. For example, enter the "Military Cargo HQ V1" (editor ID 20401) face the window with the hatch (menu close/open hatch), the "V"(="get out") command take you outdoor on top of rubbish. It seems that you can get through the wall of every 3D models with thin wall.
Camp Rogain appears to be good testing ground for this bug. It contains both cargo containers and the "Military Cargo HQ V1" mentioned, all of which can be vaulted through. Looking down towards the ground and using the Q and E keys to lean left and right while "stepping over" stuff appears to help in pushing through objects.
Also, while facing the wall of the Military Cargo HQ, you can use the "step over" key to push your weapon barrell through the wall and fire off a few shots inside! :P