The message is a multipart/alternative mime and has a text and a html part.

MIME-Version: 1.0
Content-Type: multipart/alternative; boundary=b_01_b7651919f11b2cd299ac66f79e888ff0
Date: Wed, 27 Aug 2014 14:23:42 +0200 (CEST)

--b_01_b7651919f11b2cd299ac66f79e888ff0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Text plain message

--b_01_b7651919f11b2cd299ac66f79e888ff0
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

html message

--b_01_b7651919f11b2cd299ac66f79e888ff0--

Works for me - I guess workarounds were added long time ago.