Nice. Since we're on different versions of Windows, I can totally believe that. But you only got it for one definition of factorial and not the other? Did you type them in differently somehow? (Say, by putting a newline at the beginning of the second one, or by entering the first one as the very first command of the REPL session?)
Actually, there's a chance I may be able to even though I'm on XP, since it may have more to do with the version of MzScheme being used. I'll see what I can do.