If you click the 'enter edit' button twice from the 'add artist' interface, it will create two artists with the same name.

Naturally one should be deleted automatically within 24h, but it's possible that one might accidentally select each of them when using 'relate to' or the like, necessitating a merge later on.

I'm not clear on why the second one is not caught as a duplicate (requiring a confirmation and a disambiguation comment), but obviously that should happen (or the 'enter edit' button should only take effect once.)