I've deactivated 'smooth polygons' and 'welding identical vertices' not only does not remove the problem, but introduces worse ones. Already checked. There are no identical vertices prior to import. There are no "tiny gaps"; this part of the object was modeled from a subdivided cube, the indent booleaned into it. It would be impossible for any gaps to exist if there are no spurious vertices. Let me show you a P4 renderer render from a different angle. The extent and location seems to change with it. Note the two parallel disturbances near the middle. These aren't polygons - they represent to edges of the "decal" polygon. Edges, mind you.

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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