Have not experienced this. Can you provide some proper repro steps?

I don't think this is so much a bug. However I do think that it could be more refined, along with a better damage model and the flip not being as high as it is currently.

Repro-steps seem to be drive at moderate speed into an object by the side of the road. Don't drive head on, but at an angle.
It doesn't happen every time, only on the odd ocasion you get it just right.

Unless of course you're talking about something completely different, which is not made clear by the lack of information in the post.

I think BigBigCheese nailed it. Sometime when you crash at angle, car jump like 2 meter in air and then with this jumpy up and down motion returns on ground. Its preaty much vehicle physic the cars feel realy light...

Well yes as you imagine, when u drive at high/moderate speed and if there is a mound/object on your way and if you pass over/crash it on an angle, the car reacts abnormal physics things. It may jumps couple dozen meters to up or back way.

It just happened 2-3 times to me. Not every time.

There has been an update to the PhysX engine in the game recently and also several similar issues have been fixed. Since this issue has not been reproducable, we'll consider this resolved unless shown otherwise.