When renaming an existing user to a good, free target username, I will sometimes get neither error nor success message (and returned to a now-blanked form on the Special:Renameuser page, as expected). This inevitably means the process has failed, and should be tried again. I have not figured out what circumstances make this happen; just tried it 10 minutes ago for two different users and was successful twice out of 8 attempts.

Version: unspecified
Severity: minor