When you move folders between different mailboxes in OWA, it seems that any hold related settings are simply bypassed. I really really hope there's something wrong I am doing, but so far I have been able to reproduce this in all my tests. And the implications of course are huge.
Steps to reproduce:
1) Get a user with litigation hold already enabled to login to OWA
2) Grant him Full Access permissions to any other mailbox, such as shared mailbox
3) Use the "Add shared folder" functionality to open the delegate mailbox in OWA
4) Drag and drop any folder between the principal and the delegate mailbox
5) Watch magic happens
I've tested this on several different mailboxes, including newly created ones, and in different tenants, with the same result. To illustrate the results better, look at the attached screenshots before the move:
and after the move:
Note the values for the size and number of items of the Inbox/Top of information Store subtree and the same parameters for the Recoverable Items subtree.
In contrast, moving messages between mailboxes using Outlook in Online mode will result in placing the content of the moved folder in the Recoverable Items subtree of the principal mailbox, thus should cause no problem with Litigation hold.