Cloth Renderer & Mesh collision sometimes fail

I'm using the Cloth Renderer (and Interactive Cloth) components of Unity in order to simulate a deformable inflatable ball bouncing on a moving surface.

Sometimes, the "Cloth-Renderered" ball gets stuck in the mesh of the floor. Sometimes too, it falls completely through the floor, which is a simple flat cube. (Same problem with a plane)

I have read about similar problems in this forum, and made sure all physics is being done in "Fixed Update", and not "Update". I also tried to lower the values of the "Time Manager", but without success.

Any idea what else I could try in order to make this work?

Thanks!