I have been able to replicate the problem by editing a the reference in a ppz. It doesn't matter if it is a obj or obz the fault lies in the way it is referenced. And the fact that the search done by poser for OBJ's does not include the prop library.

I removed the path from the obj reference and as it was in the same folder as the ppz poser could find it. When the scene is saved the pz3 contains just the obj name (even though it is a obz) as there is no path information and the obz is not in the same folder as the scene, poser has to do a search. Poser could not find an obj or obz in the props library. But if it is copied to the figures library or the geometries library it can be found.

Obviously when they decided to move the conforming clothing to the props library  and place obj files outside the geometries folder, they forgot to add the props library to the search. 

You could also argue  the clothing creator should have included the path in the ppz