Poser classically has always viewed figures as a collection of bodyparts, each group as a part, with weld statements to smooth out the joins on the fly. This is why morphs have a dial in each part, as well as a master dial in body.

But if you apply a subdivision function to that setup, the mesh pulls apart at the edges, the seams are visible and its a mess. You can see this if you drag an unwelded poser figure into a modeling program and subdivide it. Ugly.

So Unimesh skinning looks at the obj as one solid thing, not parts (unified mesh ... it makes sense when you think about the name) . This enables subdivision to do its thing, and give you a nice smooth clean figure. I wouldn't call it a bug per se, just a feature that doesn't work the way you wanted it.

L