Very weird. Looks like a few hours ago the name on this account changed to the email address the account is registered to. I changed it back to "Claire 

" now.
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Have you tried asking GitHub support? They're quite helpful from what I've heard, and I wouldn't be surprised if they'd put a lock on the old name - especially in cases like this where the username is/was a real name, not like anyone else would have a legitimate use for it.
Thanks. Twitter will use this to make your timeline better. UndoUndo
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sure about the name..