Messages are not received via Mailbox

I've tried the following setup:

• Briar Desktop (current main) with a temporary account
• Briar Mailbox (v1.0.5) on an Android phone
• Briar Android (v1.5.1) on the same Android phone

Steps to reproduce:

1. Connect Briar Desktop with Briar Mailbox
2. Add Briar Android as remote contact on Briar Desktop
3. Exchange some private messages
4. Disable Internet for Briar Desktop (in system-wide settings)
5. Send messages from Briar Android to Briar Desktop
6. notice that the messages is marked with the "scheduled" icon
7. Navigate out of the chat and back in
8. notice that the messages are now marked with one "checkmark" icon (I assume this means they have been sent to somewhere, probably the Mailbox?)
9. Go offline in Briar Android (disable all connections in app settings)
10. Re-enable internet for Briar Desktop
11. notice that nothing happens (the messages are not received)
12. make sure Mailbox is connected with successful connection check from Briar Desktop

Also, sending messages from Briar Desktop to Briar Android (with no own mailbox connected) doesn't work, the messages stay marked as scheduled. Am I right that it should also work in that direction in theory?