Quote - I guess I don't know how things work... but my assumption in that situation would be that a rendering engine would raise the whole polygon rather than have the middle sink.

That's obviously how the DS render engine works, and I would have thought it would be far less refined than Firefly. :-

In either app, a quad polygon can be non-planar - if a quad polygon is not utterly flat, then it is non-planar, and will be either convex or concave.  D|S uses Catmull-Clark subdivision to obtain a polygon smoothing effect, while Poser uses Reyes rendering's micropolygon subdivision.  Both of these result in non-planar polygons practically everywhere.  And many of them will be concave :)  You may not have noticed it, but I encourage you to take a harder look, it's more obvious in a modeler.

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