Not a DS user, well very occasionally, but I'm a Poser user that uses Blender to make morphs quite a bit.

When I import the model I choose do not split and keep vertex order.

When I export I only check keep vertex order.

 Maybe the original vertex order is getting scrambled? It's important that this winding order is maintained. There's Poser only scripts that record an objects winding order and rebuild it by comparing during a reimport as morph target or FBM. Not sure if DS has such.