I got mail. kmail shows its attachment above text/plain. Replying does not quote anything.
The (stripped down) content:

Content-Type: multipart/mixed; boundary=Apple-Mail-13-278331978
Subject: xxx
Date: Mon, 11 Mar 2013 07:58:24 +0100
Message-Id: <xxx>
To: Rohdewald Wolfgang <wolfgang@rohdewald.de>
Mime-Version: 1.0 (Apple Message framework v1085)
X-Mailer: Apple Mail (2.1085)
X-ID: xxx
X-TOI-MSGID: xxx


--Apple-Mail-13-278331978
Content-Disposition: inline;
	filename=130310Timo.jpg
Content-Type: image/jpg;
	x-mac-type=4A504547;
	x-mac-creator=38454C45;
	x-unix-mode=0644;
	name="130310Timo.jpg"
Content-Transfer-Encoding: base64
...
--Apple-Mail-13-278331978
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=iso-8859-1


This is the message text

--Apple-Mail-13-278331978--


Reproducible: Always

Steps to Reproduce:
1. view this message
2. reply

Actual Results:  
does not quote

Expected Results:  
should quote