Last modified: 2014-04-30 06:40:09 UTC
Account names with double underscores persist in Special:ListUsers, even though clicking on them will tell you the account doesn't exist. As a result, they can't be blocked, or hidden from the list with HideUser. See the URL for an example from en.wp
http://en.wikipedia.org/w/index.php?title=Special%3AListUsers&username=Exclamation+mark+_&group=&limit=10 still shows users that are reported not to exist when you click the links. However, I don't see the double underscores, so maybe the problem is more generic. I also wonder whether this is the fault of Special:ListUsers or the database itself, not deleting completely usernames under certain circumstances. Moving to Database component to see if we get more feedback there.
(In reply to Dominic from comment #0) > Account names with double underscores persist in Special:ListUsers, even > though clicking on them will tell you the account doesn't exist. As a > result, they can't be blocked, or hidden from the list with HideUser. See > the URL for an example from en.wp Those users appear today as blocked, so there must be a way to deal with them. Marking this report as WORKSFORME, because I have no idea whether this was fixed, or not a problem in the first place.
