I find it suspicious that it looks like it occurs on a seam. On a seam, each vertex in the preview is indeed two vertices on the same xyz position, as the parent pos is copied over the child pos to glue the body parts together. However, normal computation near seam have a problem of internally using the old individual child vertex position rather the new value set by the weld operation. Its an "issue" that can be observed down to poser 6, maybe even lower versions. I think it isnt easy to fix. not sure if there are plans to do sth about it. If he morphed the head, then i hope its repairable. For uv issues I do not know.