each object should have its own material settings and names. so check each single object
in the menu render settings, if there is a unique name for each material assigned. if not
then you may only see the name "preview".
when you export the 3 objects and re-import the combined object into Poser,
there is only one material left: "preview" and only one texture is applied to the
whole thing. I thinks this happened in your 2. render.