Hi to all and sorry for my english!

In these days I try to learn something about Maya. I start with a very simple lofted surface. But I've got a problem: if I detach the surface (see the example file link below) and I try to re-attach it the result is different from the original. How could I restore the original form of the surface?

Thanks a lot for any suggestion!!

This is my file: https://camionsauro.altervista.org/attached.mb