Last modified: 2010-02-27 16:16:24 UTC
Normally, going to the block form for (or attempting to block) an already blocked user results in a message along the lines of "Already blocked, do you want to change this user's block settings?" Going to [[Special:Block/0]], or manually entering 0 as the username, when the user is blocked does not produce this "already blocked" message, and submitting the form has no effect. To change the user's block settings one must unblock and then re-block the user.
Fixed in r63052.