Could we just call it "Login name"? This sounds really like a bad macintoshism to me -- generating nonsensical name just for sake of not sounding like a computerese -- even the Aunt Tillie these days knows what login name is, and this duo "Name/Short Name" is guaranteed to confuse everybody.
I agree, Short Name sounds awful, and doesn't seem to mean anything. "Login name" or "Username" would make much more sense.
Quasar