CreateMeshes bug?

Yes, i agree with that. Meanwhile, until this can get fixed, you might work around the problem by doing some pre-check before export like this in your script:

    # check for different count of mesh vertices and normals
    if mesh.Vertices.Count != mesh.Normals.Count:

        # get the id of the problematic brep 
        brep_id = .........
        rs.UnselectAllObjects()
        rs.SelectObject(brep_id)

        result = rs.Command("_ExtractRenderMesh", False)
        if result == True:
            mesh_ids = rs.LastCreatedObjects(True)
            mesh_id = rs.JoinMeshes(mesh_ids)
            rs.UnselectObject(brep_id)
            mesh = rs.coercemesh(mesh_id)
        else:
            print "Error extracting rendermesh"
            return False

        # use this mesh instead for export
        return mesh
        # delete the rendermesh after export

    else:
        # export as usual

c.