Yeah, I came to the conclusion that P13 does not like anything that is pre-P13 texturewise to render with graphics cards. Something with the new render engine is even more hostile to old setups then P12 was and even texture converter scripts don't help. Or are inconsistent.

It must be something with Physical vs. Cycles Surface. This may need at least a short manual/ documentation from those who understand the differences for us casual users, because it will cause quite a noise. There is a LOT more work to be done to convert to render correctly.