txt version of email based on html version is auto-generated but not recorded

When an email is sent with just an html version and no text version, civicrm automatically generates it. This is useful, but appears to be un-documented. And worse, it doesn't record the txt version in the mail record so you can't tell that it was done.

Ideally, the behavior would be, when editing an email:

• The text version would be auto-expanded, so it's more obvious that it may be blank.
• A button would be available to auto-generate the text version (and optionally edit it afterwards)