Repro has some unused stuff like MRAP or some scripts running but in general it should not be cause of a bug. I decided to leave everything in because it was difficult to make a repro for the bug and I want to provide the environment as-is.
Repro probably recreates just one of the cases of the bug since boats are affected by the bug as well yet have no wheels. Bug probably happens with boats after their propeller hits the ground. I remember that boat from the video http://www.youtube.com/watch?v=xW5gMhdWyag was taken from the shore.
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Another interconnected problem is that non-local vehicles sometimes enter rest state while mid-air. Here are examples of such problems, vehicles were driver far away from player, then player left them and apparently they kept moving and entered rest state while mid-air making it appear that vehicles fly above ground\underground while vehicle owner has vehicle properly on the ground:
http://cloud-3.steampowered.com/ugc/486682718258259592/3B87322F1014437FCF705F3F0A9E043320B48B88/
Truck got stuck in the air, its simulation was enabled, it was owned by one of the clients. Its position normalized as soon as I moved camera closer.
During attempts to make a repro for this ticket we encountered similar situation that results in vehicles being stuck mid-air: http://youtu.be/Td9Mv-Ou_kw After collisions with non-local vehicle, non-local vehicle may start flying above the ground. Sometimes it even got stuck in unnatural position above ground until you moved your camera closer, just like in observed results on live servers and screenshot above. Vehicle can be server-owned as well as client-owned, situation demonstrated in the video happened in both cases.