duplicate mailing problem

After the problems outlined in my "Help: Broken pipe error using 
majordomo" post, I found answers in:
http://www.greatcircle.com/lists/majordomo-users/mhonarc/majordomo-users.200111/msg00172.html
http://www.sendmail.org/~ca/email/smenhanced.html

Accordingly, I went ahead and set up a bulk_wrapper and ran our first 
big list yesterday, some 2500+ list members.
Everything was going tickety-boo until about 18 minutes in when a second 
parent instance of bulk_wrapper appeared and starting dispatching 
duplicates.

After the dust settled (5000+ mailings in an hour, with the server 
seemingly unloaded...big change from 100% CPU with 2-3 400 member lists) 
, problem determination seems to show that the message bounced off a 
recipient and came back to run a second time.  The original header is as 
expected, while the header in all the duplicate message shows the 
original header plus the routing of the bounce.  It appears that, since 
it bounced, it came back still as originating from the list owner (the 
only one authorized to submit messages) and thus was authorized for 
dispatch...the second time.

Note that this duplication does not appear to be:
= a queueing problem
= a bulk_mailer/wrapper fubar
= an HTML problem (plain txt message)

I searched the archives and could find nothing.

Has anyone else had this problem?  Thankfully the bounce just happened 
with one recipient!  Solutions?  Brickbats for something obvious I missed?

The duplicate header has this stuff:
================================================
Return-Path: <[email protected]>
Received: from localhost (daemon@localhost)
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) with SMTP id j7NL20n675946;
	Tue, 23 Aug 2005 21:02:00 GMT
Received: by bard.edu (blk_mlr v1.13); Tue, 23 Aug 2005 20:18:29 +0000
Received: (from majordom@localhost)
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) id j7NKISl524328;
	Tue, 23 Aug 2005 20:18:28 GMT
Received: from mercury.bard.edu (mercmailport.bard.edu [192.246.229.40])
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) with ESMTP id j7NKIQS532626
	for <[email protected]>; Tue, 23 Aug 2005 16:18:26 -0400
Received: from mailcop.bard.edu ([192.246.229.38])
	by mercury.bard.edu (AIX5.2/8.11.6p2/8.11.0) with ESMTP id j7NKIQM647186
	for <[email protected]>; Tue, 23 Aug 2005 16:18:26 -0400
Received: from aitchison.edu.pk (WL-DATA-237.nexlinx.net.pk 
[202.59.76.237] (may be forged))
	by mailcop.bard.edu (8.13.4/8.13.4) with SMTP id j7NKF6sa005543
	for <[email protected]>; Tue, 23 Aug 2005 16:15:15 -0400
	(envelope-from [email protected])
Received: from aitchison.edu.pk [66.193.188.114] by aitchison.edu.pk []
	with DomainPOP (MDaemon.PRO.v5.0.1.T)
	for <[email protected]>; Tue, 02 Sep 2003 01:12:21 -0700
X-Original-To: [email protected]
Delivered-To: [email protected]
=========================================================
below is the header that is found in the original message
bounce begins above (total header is above + below)
original header is just the stuff below
=========================================================
Received: from shell.bard.edu (shell.bard.edu [192.246.229.9])
	by one.mavsol.com (Postfix) with ESMTP id 672C59C8A3
	for <[email protected]>; Wed, 24 Aug 2005 01:12:51 -0400 (EDT)
Received: from localhost (daemon@localhost)
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) with SMTP id j7NKAiL831718;
	Tue, 23 Aug 2005 20:10:45 GMT
Received: by bard.edu (blk_mlr v1.13); Tue, 23 Aug 2005 20:02:06 +0000
Received: (from majordom@localhost)
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) id j7NK26l524346;
	Tue, 23 Aug 2005 20:02:06 GMT
Received: from mercury.bard.edu (mercmailport.bard.edu [192.246.229.40])
	by shell.bard.edu (AIX5.2/8.11.6p2/8.11.0) with ESMTP id j7NK24S708744
	for <[email protected]>; Tue, 23 Aug 2005 16:02:04 -0400
Received: from mailcop.bard.edu ([192.246.229.38])
	by mercury.bard.edu (AIX5.2/8.11.6p2/8.11.0) with ESMTP id j7NK24M1110040;
	Tue, 23 Aug 2005 16:02:04 -0400
Received: from mailweb.bard.edu ([10.20.10.26])
	by mailcop.bard.edu (8.13.4/8.13.4) with ESMTP id j7NJwt48004502;
	Tue, 23 Aug 2005 15:58:56 -0400
	(envelope-from [email protected])
Received: from mailweb.bard.edu (localhost [127.0.0.1])
	by mailweb.bard.edu (8.12.8/8.12.8) with ESMTP id j7NK20MP019786;
	Tue, 23 Aug 2005 16:02:00 -0400
Received: (from apache@localhost)
	by mailweb.bard.edu (8.12.8/8.12.8/Submit) id j7NK1xVT019784;
	Tue, 23 Aug 2005 16:01:59 -0400
Received: from user-0cdfkfb.cable.mindspring.com 
(user-0cdfkfb.cable.mindspring.com [24.215.209.235])
	by webmail.bard.edu (IMP) with HTTP
	for <[email protected]>; Tue, 23 Aug 2005 16:01:58 -0400
Message-ID: <[email protected]>
Date: Tue, 23 Aug 2005 16:01:58 -0400
From: Words Without Borders <[email protected]>
To: [email protected]
Subject: WWB August Newsletter
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
User-Agent: Internet Messaging Program (IMP) 3.2.1
X-Originating-IP: 24.215.209.235

-- 
====
Stewart Dean, Unix System Admin, Henderson Computer Resources
Center of Bard College, Annandale-on-Hudson, New York  12504
[email protected]  voice: 845-758-7475, fax: 845-758-7035