This is expected behavior by Microsoft Exchange and how it handles move requests by default.
In the release to manufacturing (RTM) version of Exchange 2010, if a personal archive exists for a mailbox that you want to move, the archive gets moved with the primary mailbox. This is because the personal archive and the primary mailbox must reside on the same mailbox database. Before moving mailboxes that have a personal archive, you should consider the size of the archive. Consider database size and how that size might impact the time the move will take to complete.
In Exchange 2010 SP1, personal archives and mailboxes can exist on separate databases. The move request cmdlets and the move request user interface (UI) in the EMC support moving mailboxes and personal archives together or separately. By default, the primary mailbox and the archive are moved together.
The Mail Synchronization Agents when tasked to move a mailbox from 1 mailbox database to another generate a New-MoveRequest PowerShell cmdlet to move that mailbox. Because the default behavior is to move both archive mailbox and primary mailbox to the same mailbox database this cannot be avoided with the use of our tool.
