Rigidbody collision is delayed[FIXED]

Update: I changed the shader on the mesh(transparant/diffuse to diffuse) and this appears to have solved the problem.

The scene is quite simple, a sphere(rigidbody) falls down in a maze(mesh collider). Yet for some reason the sphere keeps falling through the maze even with "Continues Dynamic" as Collision Detection and the DontGoThroughThings script. I've tried adding drag to slow the sphere down and adding an box collider as child to the maze, both didn't help. Tracking the OnCollision event in the sphere.

 void OnCollisionEnter(Collision c)
 {
     Debug.Log("Collision");
 }

shows that the collision does happen but when the sphere has fallen through already, so it seems to be delayed.

Anyone know what I am doing wrong? They aren't triggers or kinematic.

Using Unity 3.4