Update on bug:
I tracked down the reason for the bug.
At first, I was seeing some problems in the wingtips of a Fw190A-5 skin I've done. The textures were depcited, but the color was weird.. But the default Fw190A-5 skin didn't have any noticeable problems.
So I figured that it had something to do with material.txt settings.
* I used the material.txt from the default Ki-84-Ia skin and used in on my Fw190A-5. That gave me the wingtip problem.
* Then, at the second test, I used the material.txt file from the default Fw190A-5 skin - no problems this time.
So my take is, the new adjusted 190 wingtips has some problems with some of the material.txt settings.