If you dragged the mount icon from your partner bag to either the IS bag or backpack using click-and-hold, it might be possible to accidentally drop the icon outside one of the bag slots and not get the "do you really want to delete this item" warning. I'm not saying that this is what happened, but stranger things have been known to happen.
Since you've sent in a ticket to Support, all I can counsel is to be patient and wait for Support to respond.