Hi,
I attached an assembly (sorry but it's in SW2010 PR1), where an object in PP material is supported on a steel plate.
I add the gravity and the Contact.
In the Basic Motion the object penetrates, but doesn't fall.
In the Motion Analysis the object falls.

Where do I wrong ?
I haven't still build the object, so I can't say if fall or not, but seeing the center of mass, I don't think it can fall.