Slowing down rendering by applying submat

[fobus]

I found a strange bug that cause a huge rendering slow down. If I apply to few instances multiSub material and to some of them one of the materials from this multiSub material rendering sometimes slowing down in three times! Not always but sometimes. And when it happens materials on all instances are changing to one of the materials from this multiSub material.

[Ondra]

Looks like it is working fine in current builds. It renders also much faster now, 11.5Mrays/s on i7 2600k