Sorry my work is now two weeks under schulade!
If you try to export any object to obj format and then import it back. You'll see the same problem!!!
Why? I will answer it later and it will be a good knowledge for game modding!!! :twisted:
For now, try to detach the faces you want to have different "smooth group"! And scale those newly created vertices a tinny bit(like: 100.1%). Then you should have different smooth faces in your mesh!
Hope this help!