@Image-Edit just a suggestion because it sounds like your work-flow is going funky somewhere.

Export V4 (or whoever you are using) out of Poser and into your modeling/sculpting program and DO NOTHING! Just turn right around and export that sucker out of there. Now re-import that obj into Poser as a morph target.

If it blows up then your app is screwing with the vertice count. If it doesn't you are good to go.

If you are using multiple apps then do the very same thing as above just add one app at a time to the workflow until you find the problem.

Easy-peasy!

Comitted to excellence through art.