I can't get the U & the V channel on bsp surface to flip on anything other than than the default checkered material applied to the brush. Can anyone else confirm this?
Dumb question, but in the Preferences do you have FBX set to export smoothing? It's, for reasons beyond the comprehension of mortal man, off by default.
If it helps, the problem occurs on the bottom section of the model if it helps even more the render that I have provided is default scanline render with no lights.