Duplicate folders are created in Microsoft Exchange Server 2013 after you move a mailbox that has large or corrupted properties or after you move a mailbox by using the -IgnoreRuleLimitErrors switch.
For example, you might see Task, Task1, Contacts, Contacts1, and so on. Also, the Folder Type value may be "User Created."
This problem occurs because mailbox folder properties are removed if a property error for the Inbox folder occurs during the move. Such errors prevent migration of the default folder references for the Inbox. After migration, the default folders are re-created.
To resolve this issue, install Cumulative Update 9 for Exchange Server 2013.
To work around the problem if it is caused by the -IgnoreRuleLimitErrors switch, never use this switch together with the New-MoveRequest cmdlet in Exchange Server 2013. This switch is causing the duplicate folders problem.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
When this problem occurs, you may be able to view a list of duplicated folder by running the Get-MailboxFolderStatistics cmdlet.