Its NOT a bug.. you need to model FOR POSER, not for your modelling application.

Note pjz99's image with the cylinder with the point in the middle of the cylinder top.. that's the proper way to model a cylinder for poser rendering. Pose does NOT like ngons (faces with more then 4 points), and does not like extreme angles, or long thin polygons. Smith Micro even has that mentioned in either a tutorial or the manual somewhere.

Thats why my first question was "how many verts do the ends have?"

You need to learn to model for poser.

Way too many people take way too many things way too seriously.