Poser hates two sided polys. I know it's a pain in the butt. bit if you're modeling something thin like clothing, you'll have to make the cloth one sided and just stick to two sides at the clothing openings. If you're making something like a vase or vessel of some sort, you'll have to add enough thickness so that Poser renders it correctly. If the inside and outside are too close together, Poser does a horrible job.

Laurie