There is one easy way to check if Poser imported the object with some inverted faces.

Select the object which has the problem

Go into the group editor. The object has 1 or more groups (if not, create a new group and add all). If all the faces are correct, all should be red. If not, press Reverse Group Normals. If now all the missing faces turn up in red, there definitely is a problem with back facing polygons

At least then we know if there is a problem with backfacing polygons.

If it is, you can try to check the "Normals Forward" option in the material setting of the object