Hi There
I have the same issue as http://social.technet.microsoft.com/Forums/eu/exchange2010/thread/1bb6d578-59a4-4425-a2dd-d037fbf831dc but in my case after a database cleanup I still see the 2nd mailbox that is not accessible via GUID. We had a some corrupted mailboxes which did not want to be moved to the new database and I had to recover them from a backup and I think this is where the 2nd GUID was created or it was the old GUID for the user. I'm a bit at a loss as to what to try next. Any pointers will be appreciated. Thanks.