Quote - My first guess would be that there are some normals reversed.
When you import did you tick the "Make polygon normals consistent" option ?

It's also possible that there are double sided polygons in those areas, if you're using P6 or P7, just tick the "Normals_Forward" box on the "Poser_Surface" node of the relevant material.

 

Thanks for the suggestions, but the Normals Forward box didn't help, and it looks like I have the "Make polygon normals consistent" button selected by default.  I'm pretty sure it's a problem with the actual modeling, I just don't know how I need to change the modeling to fix it.