What's happening in this example is that the ball is gaining lots of momentum and is basically "tunneling" its way into the level geometry.
Every frame I check entity/world collisions and set up temporary collision joints to prevent the entity from moving any further. The global ERP/CFM parameters define how restrictive this joint will be. An ERP of 20,000 corresponds to ca. 20% error correction per frame. Thus if the ball is 1 quant into the wall it will be approximately 0.8 quants into the wall afterwards. But since the force is still being applied next time around the ball is 2 quants into the wall, which will be corrected to 1.6 quants, etc. At some point the ball's center is inside the block and there's no hope left.

I mentioned an additional safe-guard before. Every entities center is checked whether it has crossed a wall or not. This, however, only prevents an object from missing a wall entirely. Thus if an object shoots across the room and it would penetrate a wall, A6 puts it roughly in front of the wall and the usual joint mechanism kicks in (not in this case though because the joint is too weak).

Solutions:
- higher ERP value (and lower CFM) to enforce walls more strictly
- phent_setmaxspeed to prevent objects from getting too fast
- larger objects
- more elasticity /more friction / more damping

I will look into setting different ERP values per object or per constraint.