Cannot lookup transactions for unpinned private messages on recipient side

Steps to reproduce:
1. In a FireFly stack with 2 members, send an unpinned private message from one member to another
2. Check the value of the property "tx" in the "message_confirmed" event emitted on each of the FireFly instances (they should match)
3. Open the GUI of the FireFly instance from which the message was sent and lookup the transaction using the value from step 2. The transaction should appear in the UI
4. Open the GUI of the FireFly instance to which the message was sent and lookup the transaction using the value from step 2. The transaction does not appear