Here's what the preview window looks like when the bottom of the wings are shown. There's no doubt about the problem being reversed normals. There's a way in P5, in the Material Editor, to link to some nodes to fix the problem, but I can't remember the solution. It's a pity that the solution was never added to the manual and even more of a shame that it was never fixed in P5.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon