Nothing has been done to fix it or even diagnose it, so it ain't fixed.

This seems to be fixed, I've just received a normal mail message from
tracker issue543 today. no empty line and no empty subject any longer

I was just about to report this issue, too.

Yes, the mail headers are getting a blank line stuck in the middle of
them.  For example, here are the headers from Steve T's update
yesterday to issue395, slightly edited to hide personal email
addresses.

Return-Path: <...@xemacs.org>
Received: from gwyn.tux.org (ident-user@gwyn.tux.org [207.172.156.132])
	by mail1.rawbw.com (8.14.2/8.14.2) with ESMTP id n61AbjWL086620
	for <...@rawbw.com>; Wed, 1 Jul 2009 03:37:50 -0700 (PDT)
	(envelope-from ...@xemacs.org)
Received: from turnbull.sk.tsukuba.ac.jp (turnbull.sk.tsukuba.ac.jp
[130.158.98.81])
	by gwyn.tux.org (8.12.11/8.12.11) with ESMTP id n61Abi37028446
	for <...@xemacs.org>; Wed, 1 Jul 2009 06:37:44 -0400
Received: from localhost ([127.0.0.1] helo=turnbull.sk.tsukuba.ac.jp)
	by turnbull.sk.tsukuba.ac.jp with esmtp (Exim 4.69)
	(envelope-from <...@xemacs.org>)
	id 1MLxCB-0007GJ-Gn; Wed, 01 Jul 2009 19:37:43 +0900
Message-Id: <E1MLxCB-0007GJ-Gn@turnbull.sk.tsukuba.ac.jp>
From: ...@xemacs.org
Date: Wed, 01 Jul 2009 19:37:43 +0900
X-SA-Exim-Connect-IP: 127.0.0.1
X-SA-Exim-Mail-From: ...@xemacs.org
X-SA-Exim-Scanned: No (on turnbull.sk.tsukuba.ac.jp); SAEximRunCond
expanded to false
X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by
milter-greylist-1.6 (gwyn.tux.org [207.172.156.133]); Wed, 01 Jul 2009
06:37:45 -0400 (EDT)
X-Virus-Scanned: ClamAV version 0.88.4, clamav-milter version 0.88.4 on
gwyn.tux.org
X-Virus-Status: Clean
To: undisclosed-recipients:;

From nobody Wed Jul  1 10:37:43 2009
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Subject: [issue395] Allow for more than one site to be searched for packages
To: ...@xemacs.org, ...@xemacs.org
From: "Stephen J. Turnbull" <xemacs-tracker@calypso.tux.org>
Date: Wed, 01 Jul 2009 10:37:43 +0000
Precedence: bulk
X-Roundup-Name: XEmacs Issue Tracking System
X-Roundup-Loop: hello
X-Roundup-Version: 1.4.8
MIME-Version: 1.0
Reply-To: XEmacs Issue Tracking System <xemacs-tracker@calypso.tux.org>
Message-Id: <1246444663.5.0.89702396909.issue395@xemacs.org>
X-Roundup-issue-status: verified
X-Roundup-issue-severity: inconvenience
X-Roundup-issue-module: core code 21.4, core code 21.5
X-Roundup-issue-priority: normal
X-Roundup-issue-platform: N/A
X-Roundup-issue-type: feature
Content-Transfer-Encoding: quoted-printable

See also issue539.