Sandbox refresh boofing!?

Came across an issue from refreshing a sandbox, when it completed it had appended a bunch of extra characters at the start of all the usernames.  The refresh completion email indicated that the usernames had to be unique across all sandboxes.  For some reason it thought the usernames were already taken. This was strange since we don't currently have another sandbox with the same name.  But did have a sandbox by that name in the past.  Sfdc premier support's explanation was that boofing occurred during the copy process and suggested the box be refresh again.  Something to watch out for if you're not able to get in to a newly refreshed sandbox, particular when deleting and reusing the same sandbox name.