rmail-reply produces incorrect mail header

[enno]

Dear emacsers,

For some time now (starting with emacs23.3) I sometimes experience that 
rmail-reply (or supercite, or feedmail, or whatever) produces an incorrect 
`To:' field.  Apparently this only happens with mails from certain senders (my 
father for instance).

In the past I just deleted the `In-reply-to' header from the reply before 
sending it, ugly but worked -- unless I forgot to delete...  I'm afraid I'm not 
sufficiently familiar with elisp to figure that one out on my own.

To me it seems that somehow the header tag `In-reply-to: ' gets lost, resulting 
in a `To: ' header followed by an `In-reply-to' header WITHOUT header-tag in 
the following line.  But as stated above, this only happens with certain 
senders, others who supply `In-reply-to: ' as well work without trouble.

>From theory to practice:

Original mail received from my dad has headers like so:

v--------------------------------------------------------------------------
>From father@mailhost.xx  Fri Apr 15 15:21:32 2016
Return-Path: <father@mailhost.xx>
X-Original-To: enno@localhost
Delivered-To: enno@localhost
Received: from tapas (localhost [IPv6:::1])
        by tapas (Postfix) with ESMTP id E120F341D7A
        for <enno@localhost>; Fri, 15 Apr 2016 15:21:31 +0200 (CEST)
Received: from pop.gmx.net [212.227.17.185]
        by tapas with POP3 (fetchmail-6.3.26)
        for <enno@localhost> (single-drop); Fri, 15 Apr 2016 15:21:31 +0200 (CES
T)
Received: from some.mailhost.xx ([aaa.bbb.cc.d]) by mx-ha.gmx.net (mxgmx013) 
with
 ESMTPS (Nemesis) id 0Lgut4-1bW5BP0taY-00oDoQ for <enno.vet@gmx.net>; Fri, 15
 Apr 2016 11:00:33 +0200
Received: from [zz.yy.xxx.ww] by acertain-web.server.lan (via HTTP);
 Fri, 15 Apr 2016 11:00:32 +0200
MIME-Version: 1.0
Message-ID: 
<trinity-e2fa2971-abde-4db8-8310-6a2bc9938e25-1460710832760@acertain-web>
From: father@mailhost.xx
To: enno <enno.vet@gmx.net>
[...]
^--------------------------------------------------------------------------

I hit `r' to reply, and what I see seems perfeclty sane:

v--------------------------------------------------------------------------
From: enno <enno.vet@gmx.net>
To: father@mailhost.xx
In-reply-to:
        
<trinity-e2fa2971-abde-4db8-8310-6a2bc9938e25-1460710832760@acertain-web>
        (father@mailhost.xx)
[...]
^--------------------------------------------------------------------------

But what is sent out to my smtp smarthost (and thus causes a bounce) looks like:

v--------------------------------------------------------------------------
>From enno Fri Apr 15 15:53:24 +0200 2016
Date: Fri, 15 Apr 2016 15:53:24 +0200
Message-Id: <1557-Fri15Apr2016155324+0200-enno.vet@gmx.net>
X-Mailer: emacs 24.5.1 (via feedmail 11-beta-1 I)
From: enno <enno.vet@gmx.net>
To: father@mailhost.xx
        
<trinity-e2fa2971-abde-4db8-8310-6a2bc9938e25-1460710832760@acertain-web>
        (father@mailhost.xx)
[...]
^--------------------------------------------------------------------------

TIA for any input,

brgds, Enno.

-- 
      //       enno.vet@gmx.net
    /\\\       Mag. Enno Deimel
  .\    o
 \\  \ _  \    Wisely and slow; they stumble that run fast.
\\\     \_/
gpg-fp: eefe b049 6fe6 fc0b 0ec4  f39e af6a c178 eb98 909a