"Edit as new" loses HTML formatting

1. Set account to plain text mode
2. Compose a new email
3. Set editing mode to rich/HTML
4. Send the email
5. Go to the sent mailbox
6. Click *Edit as new* on the sent message

### Expected behavior
Editor is set to rich/html despite the account preference


### Actual behavior
Formatting is lost


### Mail app

**Mail app version:** v1.9