I believe it's a bug too. Here's a view of one of my dresses that I posted at PoserPros - this works in Poser 4, but splits open in Poser 6. I eventually "fixed"* it by changing the grouping slightly - I moved a couple of polygons from one group to the adjoining one. * The quote marks? Well, I haven't really fixed it, just made the problem go away; not the same thing. I'm convinced there was nothing wrong with the mesh, but I think I can still lay my hands on the old one if anyone wants to have a look.