Mailbox Move: Disconnected Mailbox remains on source Mailbox Store

I faced this issue while moving the mailbox from one mailbox store to a mailbox store on another server.
The mailbox is moved successfully and the user can access it fine on the server it was moved to.

However, the mailbox remains on the source mailbox store in a disconneced state and has small size. The number of items are shown as 0. The mailbox is disconnected and it does not allow you to purge or reconnect it to another user giving the message "This mailbox is already connected to a user."

To be able to purge the mailbox from the Target Store, try to move the mailbox back to that (original) Store. Move Mailbox will fail and gives you the message:

"A duplicate mailbox was found due to problems during a Move Mailbox procedure. The duplicate mailbox has been deleted. Try again later."

Hence when you run the cleanup agent on the original source mailbox store... that duplicate mailbox will be purged.

Reset the language for the folder names inside the Mailbox

In Exchange 2000/2003, when one of the following conditions takes place, the default language names of the folders inside the user's mailbox might change and names of standard folders in an Exchange mailbox, such as the Inbox, Sent Items, Public Folders, and so on, appear in different languages when seen from the client program:

1. You move a mailbox from one Exchange server to another Exchange server.
2. You create a new mailbox.

Exchange creates the folders based on the language of the Outlook client that first touches the mailbox, or the language of IE if OWA is first to touch the mailbox.

To reset the folder names, here is the registry tweak

In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\11.0\Outlook\Setup, create a DWORD value ResetFolderNames and set its value to 1.

Here is more information about this from Microsoft.