Hello again...

Now I found the cause, but no cure for it.

 I build a box with a whole in it by extruding splines, as seen above. (So far it looks perfect in Poser). Now I try to expand this hole on the backside by moving some single points in the mesh, suddenly the reflecting angle of some surfaces on the frontside is disturbed. Not to be seen in Cinema, but when imported in Poser. The speculars of nearby polygons point in different directions ! These are the bright stripes to be seen in the illustration. Normals have still the same direction but the polygons seem to be horizontally mirrored.

A speciality of Cinema R12 ?