Collison detection problems with .difs

Ok, I just noticed this, if you set the player to jump at a extreme impulse, like say 800 they will jump thru the tops of .dif objects. Specifically the small houses in RW. In the towers it seems that the ceilings are high enough that the collision detection catches it in time. But there is a catch there also, if you keep jumping and kill yourself and jump one last time after you are dead, you respawn in the air way above the spawn point!