Well, I tried exporting the mesh from Poser as a 3ds file, taking it into Rhino, exploding it, removing the end wall, replacing the wall with a plain box, creating a new obj file, taking that into Poser and thence into Vue, and lo and behold the problem still occurs. It doesn't seem so bad as it was before though. I think the trouble may not be with booleans but meshes with no thickness. That end wall seems not to have been a boolean, because the sides of the opening were individual surfaces.