[General Abe]

Unoccupied vehicle sync is client-side, a hacker can manipulate unoccupied vehicles as he pleases (causing the 'tornado' effect).

I remember this happening in 0.2x quite a lot when drivers alt-tabbed inside their vehicles and were jacked - the alt-tabber would tab back in and regain control of their vehicle, fighting against that of the new driver. Probably something similar at work here...