We've set up shared folders to manage shared mailboxes by members of a team. Every team member has their own personal mailbox, but also has access to the team-mailbox which is shared using the Zextras "shared folders" feature. Mail client in use is (mostly) Outlook 2016, and I'm currently testing on Outlook 365 (from the office 365 suite), but behaviour is the same.
All is running smoothly, except when messages are moved between the personal mailbox and the shared folder (by dragging them in Outlook). It looks like Outlook somehow creates a copy of the message (on the client-side), and places it in the destination folder, and removes the message from the original folder. However, it looks like Zimbra is moving the message as well.

sync.log says:
2019-05-10 12:39:31,510 INFO  [ZeXtras Mobile] [tid=101945;account=demo1@demo.<domain removed>;accountId=f1672495-f7ed-4be9-bb3b-bb06c9cbfbdd;id=516A263368294A5DB9865B8ED2E83128;model=WindowsOutlook15;proxy=;oip=<remote ip removed>;eas=14.0;rid=74067;] sync - Moving the item 380 to folder shared Demo 2's Inbox(2-323) for demo1@demo.<domain removed>
This results in 2 of the same messages in the destination folder in Outlook. However, when opening zimbra's web app, only 1 message is showed. Perhaps because of the one copied by Outlook has trouble syncing to the server, since it already exists or is otherwise unknown to the sync process.

The right way to fix this seems to prevent Outlook from copying the message and let Zimbra handle this, but this is not something that is user-configurable accoring to my knowledge.

Versions in use:
Zimbra: 8.8.11
Zextras: 2.14.1

Is this a bug, and if so, is there any chance this can be fixed somehow?