I've looked a little more into the problem - first I answered my question from the last post by RTFMing (sorry for that :-/) and am now using the "Set angle" functions where appropriate. But that didn't resolve the problem.
The actual problem is that I control the whole car physics, e.g. before every time step, I'm manually setting speed and direction and so on. When a collision occours, the vehicle is somehow rotated/decelerated, but my code immediately accelerates it back in the next timestep. This is *bad*.
Does anything come to your mind except resolving all vehicle/xyz-collisions manually? That would, I imagine, be kind of hard to do...