marco, in my example the problem isn't noticeable anymore with the current erp/cfm settings (although if i really try hard i still can let the ball fall through level geometry).

i first thought jason did apply too high forces but i easily could reproduce it in my levels. if a ball is forced against a wall it starts to spin faster and faster (it doesn't matter if you use a force or a torque to move the ball) and then it moves inside the level geometry.