bug#38382: 26.3; Message body not displayed after editing in rmail-mode

["Edward J. Sabol" via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> 1. Send yourself a text/plain email that has no body and no MIME attachments.
>> 2. In Rmail, retrieve the email, adding it to your Rmail file.
>> 3. Hit "e" to edit the message that has no body.
>> 4. Add a body to the message.
>> 5. Hit C-c C-c to finish editing. The body text you just added disappears!

Eli Zaretskii replied:
> I cannot reproduce this.  I see the added body after "C-c C-c" (with
> the current master branch of Emacs).
>
> How did you "add the body", precisely?  Please show the exact text you
> typed between 'e' and 'C-c C-c'.

(Sorry it has taken me a month to reply. December was hectic with all the
holidays.)

Well, maybe this is fixed in the current master branch of Emacs, but I can
reproduce it with Emacs 26.3 started with 'emacs -Q'.

After typing "e" in eithre the rmail-summary buffer or the rmail buffer, the
exact keypresses I type are:

M->

This is a test.

RET

C-c C-c

According to describe-key-briefly, M-> runs the command end-of-buffer when
editing a message in my rmail buffer. After hitting 'C-c C-c', boom goes the
dynamite, the text "This is a test." just disappears. If I kill the rmail
buffer and re-open it, I see "This is a test." So it's there. It's just not
visible after I finish editing. So I guess you could say it's cosmetic only,
but it's very confusing. Again, if the message already has a body, there is
no issue with editing it. I only see this problem with the message has no
body to start with and I add one. And "This is a test" can be any text
really.

Thanks,
Ed