I think the problem with the Poser primitives is that they have no material defined in the obj (usemtl). When no materials are defined for the individual groups, then everything uses "Preview". Same thing will happen if two or more meshes use "metal" as the material, when you reimport them as one obj, they will use the same texture and colour etc, even if diffrent textures and colours were applied before you saved them. In other words each group in what you are saving needs a diffrent material assigned to it, if it is to use a diffrent material when reloaded. The "group" names don't matter, you can have as many groupes as you like using the same name as long as each uses a diffrent "usemtl" name. But if you are loading the meshes from the Poser library pallet, you don't get the option to assign a material unless you first create a new group. If you import the mesh you can assign new materials to existing groupes.