Ball jumps instead of rolling

[bmueller]

I try to build a simple simulation: Several box objects (btBoxShape) build a tiled floor (all on the same level) on which a ball rolls (btSphereShape). The boxes are packed close to each other (0 space in between) but not overlapping.

I move the ball by changing the gravity vector: z=-10 stays the same, x and y are adjusted to the amount the ball should roll in a direction.
This means that there is always a gravity force in negative z order "down".

The strange thing is that if I move the ball fast it elevates in positive z-order.

So my question is: Why is the ball jumping? Is it because of the edges of the boxes?

I tried to let the boxes overlap but even this does not help.

[bmueller]

I replaced the boxes by triangle meshes - now everything is fine.
It seems that the edges of the boxes created the problem.