[mu4e bug] Wrong timestamp for drafts with discarded edits

[88-percent]

Describe the bug

Date field for draft messages doesn't reliably update for a very specific use case: where a draft message has discarded edits.

This causes these messages to display an incorrect date upon send - including to recipient.

How to Reproduce

1. create a new message (M-x mu4e-compose-new)
2. draft new message
3. save message as draft (M-x message-dont-send)

-- practically some time would elapse here --

4. locate draft message
5. edit message (M-x mu4e-compose-edit)
6. choose account
7. make edits
8. discard edit (M-x message-kill-buffer)
9. message modified; kill anyway? (y or n) - y
10. remove the backup file too? (y or n) - y

-- practically some time would elapse here --

11. locate draft message again
12. edit message (M-x mu4e-compose-edit)
13. choose account

Expected behavior: the message is opened in compose mode with all info the same as when it was saved except the date field which should be populated with the current time & date.

Actual behavior: the message is opened in compose mode with all info the same as when it was last saved - including the date field which is the time and date the message was last saved.

Environment

Emacs: 29.4 Spacemacs: 0.999 mu: 1.12.5 OS: Pop!OS 22.04

Checklist

• [x] you are running either an 1.10.x/1.12.x release or master (otherwise please upgrade)
• [ ] you can reproduce the problem without 3rd party extensions (including Doom/Evil, various extensions etc.)
• [x] you have read all of the above

I'm running Spacemacs so I'm unfortunately unable to disable Evil for testing. I've tried to run the above without using evil commands.