I'm fairly certain that it's a glitch, and that it isn't supposed to happen. In any case, contacting a staff member would probably be the best thing to do, if this thread doesn't do the trick.
Talk to an admin about the issue, preferably Zise as he is the one in charge of the Premiums and such. If my memory is correct, the username change plugin is prone to mishaps and glitches thus why admins still manually edit the names. And, if again I'm remembering it right, you can change your name once a day.