Last modified: 2010-02-27 16:16:32 UTC
Submitting the unblock form with '0' as the user name results in the message "Error: Block ID not found. It may have been unblocked already.", even when the user exists and is blocked. This means that unblock links from anywhere except [[Special:BlockList]] do not work. (The block list passes the block idm rather than the username).
Fixed in r63052.