1.5.1 email issue (wp_mail)

In 1.5 I had problems with the mails sent by wordpress. This could be solved by changing the following line in “/wp-includes/functions.php”
return @mail($to, $subject, $message, $headers, $more);
to
return @mail($to, $subject, $message, $headers);
In 1.5.1. the wp_mail function can be found in “/wp-includes/pluggable-functions.php”. But there’s already the line:
return @mail($to, $subject, $message, $headers);

Nevertheless since the upgrade to 1.5.1. I have the problem, that parts which belong to the mail header can be found in the message. My spam assassin doesn’t like that too much:

From: "Udo" <info@unkenntlichgemacht.invalid>
Content-Type: text/plain; charset="UTF-8"

Message-Id: <20050511134347.256AC404C12@p15161244.pureserver.info>
Date: Wed, 11 May 2005 15:43:47 +0200 (CEST)
X-Spam-Checker-Version: SpamAssassin 3.0.2 (2004-11-16) on
win2k3server.gierkezeile.local
X-Spam-Level: ***
X-Spam-Status: No, score=3.4 required=5.0 tests=BAYES_50,MIME_8BIT_HEADER,
SUBJ_ILLEGAL_CHARS autolearn=no version=3.0.2
Return-Path: wwwrun@unkenntlichgemacht.invalid
X-OriginalArrivalTime: 11 May 2005 13:43:54.0447 (UTC) FILETIME=[790FFDF0:01C5562F]

New comment on your post #170 "S/MIME-VerschlÃŒsselung mit Thawte"

… and then there’s the rest, but without the right encoding.

With 1.5 mails started with the “New comment…” line.

Any ideas?