A mailbox is placed into a mail collection and the mail is migrated to the target domain and placed into an information store. At a later time, either before the mailbox is switched or after, this mailbox is moved to a different information store in the target manually. Shortly thereafter the mailbox moves back to the original information store.
This is caused by remaining mail files still being processed by the mail target agent.
If a target mailbox is moved to a different information store before all queued mail files are processed, the mailbox will be moved back to the location specified within the mailbox collection by the agent.
No mailboxes should be moved until all prv files are fully processed for the mailbox and they have been switched via either manual or automatic methods.
To determine and view the remaining mail files in the target queue please install the Quest Migration Manager Resource Kit, and use the Service File Viewer. Either wait until all the .prv files are processed, or delete the remaining files. The Resource Kit is included on the QMM CD or download in the "QMMEX Reskit" folder.
Attached is the .pdf for the Migration Manager Exchange Reskit, which includes instructions and a description of the utility.
** Please note that deleting the .prv files can result in the loss of mailbox data, folders, permissions etc **