In MediaWiki messages that display usernames, if the parameter input is numerical, the software assumes that it must be a user id. This breaks the message for users with purely numerical usernames.
This bug came to light after [[User:7]] on the English Wikipedia blocked themselves for April Fools, but the blocking user was displayed as [[User:Joao]] (user id 7). See the following:
https://en.wikipedia.org/wiki/MediaWiki_talk:Blockedtext#.241_variable_is_not_working
https://en.wikipedia.org/wiki/File:Blocked_Media_Wiki_Parameter_Problem.png
Version: 1.22.0
Severity: normal