message moved to deleted items after pressing discard

Hi,

We are experiencing a strange phenomenon in Outlook 2013.
We share a mailbox with several people and once a while when selecting a message in the inbox it's possible to edit the original message.
When choosing discard, the message is moved to the deleted items of the users mailbox. Resulting in message loss from our shared mailbox.
Also an icon with a notepad and pencil is placed in front of the message affected as you can see in the screenshot below.

Best Regards,

Bart Crommen