Forwarding marks as read but leaves Mark as Read button in toolbar

Expected behavior

When I open a message, mark it as unread, and then forward it, it gets marked as read again once the compose forward activity appears, but after sending the forward and returning to the original message, the toolbuar still has the Mark as Read button in it, rather than Mark as Unread.

Actual behavior

Either the message should not get marked as read as a consequence of opening the composition activity, or the toolbar should contain the Mark as Unread button (because the message is by that point read) rather than Mark as Read.

Steps to reproduce

1. Open a message.
2. Use the toolbar to Mark as Unread.
3. Confirm that the toolbar contains the Mark as Read button, as expected.
4. Issue the Forward command.
5. In the composition activity, send the forward e-mail, thus returning to reading the original e-mail.
6. In the toolbar, observe that the Mark as Read button is still present.
7. Back out to the containing mailbox and observe that the message is actually read, not unread.

Environment

K-9 Mail version: 5.800

Android version: 8.1.0

Account type: IMAP

Start by reproducing the forward flow described in the issue on Android with K-9 Mail 5.800, observing the toolbar after sending and returning to the original message. Trace the read-state and toolbar update around the forward composition activity. Done means the toolbar and containing mailbox both reflect the message's actual read state.