It could also be double-sided polygons.
Lines in Poser-4 renderer, big square blotches in Firefly? If so, that's (probably) double sided polys.

Neither of Poser's renderers like 2-sided polys, especially if there's a texture attached.
The reason seems to be that the renderers are expecting single sided polys (so that they know "which way is out"). With 2-sided polys they have a hard time making their minds up, and keep changing sides.

The "displacement" trick in Firefly works 'cos it creates a distinct difference between the 2 sides. Alas, nothing can be done for the P4-renderer (AFAIK).

The only permanent solution is to import the object into a 3D modeller and make it 1-sided there (and then check that all normals are facing outwards), and re-export.

Cheers,
Diolma