mutually affecting collision with different forces, kangaroo?

i am trying to drop a box onto an inflating bubble quite similar to Daniel Pikers video 
http://vimeo.com/11790443 

i managed to deform the bubble with the box as it drops, but the box does not get with affected by the collision and falls all the way through onto the ground.
i cannot get the objects to mutually affect each other, i feel it would get recursive since one deformed geo should be the base for the collision with the other and likewise. would i need to loop anything? does anybody know what i am doing wrong here?

Thanks