That’s odd. It calls UserNameSuggester, which should suggest a valid username in almost every case. Did you see errors during the import?
It sounds like the users are being created (looks like the right number) but that there’s a problem matching the users to the new usernames.
I don’t recommend that.
Thanks! That’s very helpful. I’ve got a tweak to the permalink code that I recently submitted. Perhaps I’ll add this bit in when I get around to that.