Did you do your tests on terrain? Since everything works fine on block geometry. About the jittering, yes I've observed it many times, and it needs to be fixed. This isn't jittering though, since the last physics entity enabled actually intersects the terrain and goes down about 1/3rd then pops back up - only to repeat itself agian. Of course, I guess I can just apply the physics engine to some rock out in the middle of nowhere last, that way it will have the faulty collision and everything else will be good.