Please be aware of an emerging issue in Exchange 2013 and Exchange Online. In a delegate scenario it is possible that OWA can be used to delete a folder from the other user's mailbox and not appear in the Deleted Items section of the recoverable items folder.
This is covered in KB 2996477 — Folder deletions are not preserved for mailboxes put on litigation or in-place hold in Exchange Server 2013 OWA.
Update 15-9-2014: Bharat tweeted that the Office 365 fix is being rolled out and CU7 is the target delivery mechanism for on-premises customers.
Consider the following scenario:
You are using Microsoft Exchange Server 2013 or Microsoft Office 365.
In this scenario, you have two users, User A and User B.
User A's mailbox is put on a litigation hold or in-place hold.
User B's mailbox is not put on a litigation hold or in-place hold.
User A designates User B as a delegate to User A's mailbox.
User B uses Outlook Web App (OWA) to access User A's mailbox, and deletes a folder from User A's mailbox or moves the folder to User B's mailbox.
In this scenario, the deleted or moved folder items do not appear in the "Deleted Items" section of the Recoverable Items folder.
Please monitor the KB for updates and progress on this issue.