Upgrade from 3.3 to 3.4 physics problems

I am working on a gravity / physics based game where the player controls a spaceship. The game is a 3D game, but the gameplay is constrained to a 2D plane to give the feeling of a retro game. I am using a joint to constrain the ship to the XY-plane movement-wise, and constrained to the Z-axis for rotation.

In Unity 3.3 all was working as intended, but when I upgraded to 3.4, and 3.4.2 there are problems when the ship collides with other objects. Basically it gets blasted around the level as if it had no masss. Mostly this happens when colliding with other objects that are static (walls), but also with other moving objects.

Does anyone have any idea what could cause this?

Update: After I posted I found this thread. Base on the advice in there I removed my configurable joint and added the constraints to my ship's rigidbody. Seems to work fine.

It's more of a workaround than a solution, but atleast my game now works in unity3.4+ :-P