Hi Dirk, I suspect what you are seeing there is probably a side effect of the way that C4D decided to triangulate that n-gon.

Let me illustrate - say you have this 5 point n-gon:



Now say to produce a triangulation of this n-gon, what if the triangulator starts by placing this triangle:



Then next it places this triangle:



It certainly looks like the triangles it picked were nicely shaped, but it is actually pretty bad because now it only has one possible point left to form the last triangle, and it will be a degenerate one along the side there:



It is not uncommon for triangulation mechanisms to have this problem in them when processing n-gons shaped like that. Some algorithms tend to get led astray because those initial triangles seem nicely shaped, so it starts peeling away those but then ends up with a bad one at the end.

MoI's triangulator goes through some pains to not produce this kind of thing, so that's why you don't see the problem when you export using the Quads & Triangles option in MoI.

I have not reviewed your files yet to verify, but it is pretty likely that is your problem and the black shading is some side effect of the triangle being degenerate when it was created by C4D.

Tomorrow I'll double check your file to verify if this is the case or not. If it is, then I'm not really sure what I can do about it - it would really depend on C4D improving their triangulation mechanism to not create degenerate triangles in situations like this. I guess I could try to avoid creating this kind of shape, but that would probably mean slicing out points that are needed to make the polygon outline appear curved within the angle tolerance...

- Michael