My piece goes through its support in Motion analysis

Hello

I am trying to make a study of the movement of a cupola resting on 3 balls.

I set up the constraints with a tangency of each of the balls with the inner face of the dome  and at the "model" level my dome moves as I want it to on the upper surface of the balls.

I created a new motion study and I created a contact function type 'Solid body' between the 4 elements, and I added gravity.

But when I run the motion analysis, my cupola passes through the marbles in such a way that the upper part of the cupola is tangent with the lower part of the marbles.

Ok, the constraint is still valid but it's obviously not what I want.

Why this behavior?

Alan