Strange, I have render cow problems, but not this one. You should report to E-on, that's what I do, and hope they fix the problem with the next update. BTW, my problem is that rendered tiles don't well... tile! Seams are visible, and the lighting/shadows/colours are different from one tile to another. Happens sometimes, randomely. Why do we have to pay so much money for high end software and wait for patches to correct numerous bugs?