Speaking from a point of extreme ignorance, if the model coming back into Poser was invalid (eg vertex count) would not we get a "import prop" prompt? I've always assumed a morph is a series of deltas applied to the base mesh rather than an actual mesh in the scene, if this is the case are we talking about the calculations of these deltas going wrong? I've not been able to reproduce the error to test this idea but have only been using basic disp brushes like snake hook, will try with brushes mentioned above.