I, too, was under the impression that usernames must be unique. Yes, those are certainly duplicates, according to super search: https://perlmonks.org/?node=OliviaB.

I have an inkling that username sanitation happens at the wrong time during registration, like removing a space at the end after the database has been checked for duplicates. But that's pure speculation at this point. I'll have a quick peek in PmDev, but i doubt i'll find anything on my own...