Last modified: 2009-03-11 18:12:12 UTC
Apparently, any username containing a : cannot be blocked by administrators. Case in point, [[Special:Contributions/WP:ANI]] on enwiki.
The user account can be renamed. And I believe this is related to namespace aliases (WP: and WT:) not colons. Summary adjusted accordingly.
In the golbal block form you can use "#<USERIDNUMBER>" in the username field, that might also work in the local block lists as well.
*** Bug 17878 has been marked as a duplicate of this bug. ***
See also, Bug 17879 which points out that User:WP:ANI was only created because CentralAuth allowed a name to be created that would have be forbidden if one attempted to registered it locally. I filed that separately because at least in principle one could patch this bug without tackling the AuthPlugin issue, but I believe it probably makes more sense to disallow AuthPlugin from creating accounts that lead to this scenario. If one does patch AuthPlugin it would be very difficult (though not strictly impossible) to arrive at this bug again.
Modifying to a correct description of the problem
Fixed for autologin in r48211. WORKSFORME in core login interface.
*** Bug 17879 has been marked as a duplicate of this bug. ***