The scene setup goes like this:
I have a simple box, each side has a different ID, when i add multisub object material with arch&design materials to the sides with different reflection settings and textures to drive glossiness/reflecion color/bump and add couple of lights the sides of the box become kind of semi transparent, when i render the front of the box, i can see the other side of the box in the black parts of the front side's reflection. when i turn off the lights everything is fine, when i add standard material (not arch&design) it is also fine. I think it has something to do with reflections, when 2 reflections on multisub object are calculated on top of each other they are visible through the mesh. But i can be wrong, if so, please correct me and help me find a solution to this problem.