I don't know anything about Lightwave, but I suspect your problem has to do with how the mesh is grouped into subpatches as you say.  Are you exporting the entire mesh and importing the entire mesh back into Poser?  Or when you export a morph target, are you only exporting the subpatch?  It sounds like you're exporting "a bodypart", which suggests a subpatch - possibly the border verts are not counted quite the same.  Do border verts exist in both bodyparts as the same vertex, or two separate verts that are in the same x/y/z?  If Poser is saying wrong number of verts, that may be why.  You probably would have better luck asking in a Lightwave forum, as you say.

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