I'm currently running into an issue where an object I made has sort of a flipped highlight and shadowing.
Note the sun direction and the shadows from tracks, but that the backside of the train car is also still bright. In contrast, the other side of the train car is all dark.
My work flow has generally been from whatever modelling program->OBJ->3dsMAX->OBJ ->Milkshape->TSRW Object->TSRW->S3Package.
A special note is that there is no actual shadowing generated for the mesh, since it replaces an effect and effects do not cast shadows.