Special:AutoLogin is creating local accounts and merging them when they don't exist. It's not meant to do that. It's causing problems in conjunction with T16862, i.e. total breakage of Special:RenameUser. It also floods the logs. This is apparently a regression.
- user registers on ru.wiki: local and global account are created;
- user logins on wikimania wiki and the local account is automatically created;
- as a side effect, 13 accounts are created at the same moment on all English and multilingual wikis.
Step 3 does not happen.
See also: not to be confused with T21161: Don't autologin if local account doesn't exist (don't autocreate if user doesn't explicitly login)