I believe that the problem has to do with conflicting orientations set
by the exporter. The exporter sets the face_orient field of all faces
to 1, but since it also sets the edge_orient field of all of the edges
to 0, the importer reads the wrong orientation of the edges. I am not
absolutely certain as to what the standard menas on this point, but I
believe that this could be fixed in the importer or the exporter ---
if the importer either set face_orient to 0 or the edge_orient fields
to 1 the behavior would be fixed (face_orient is set on line 1803 of
iges.c, edge orientation is calculated on lines 1706-1709 of
iges.c). Also, a similar fix could be created by inverting either the
face_orient or the edge_orient values in any of
Get_outer_shell/Add_inner_shell, Add_face_to_shell, Make_planar_face,
or Get_vertex.