What steps will reproduce the problem?
1. Install Trac 0.12 using mod_python or mod_wsgi on Apache
2. Test performance
3. After several clicks, the site hangs

What is the expected output? What do you see instead?

Normal page loading speeds. Commenting out the line:

LoadModule pagespeed_module /usr/lib/httpd/modules/mod_pagespeed.so

causes Trac to behave normally again.

What version of the product are you using (please check X-Mod-Pagespeed
header)?

mod-pagespeed-beta-0.9.0.0-128

On what operating system?

CentOS release 5.5 (Final)
Linux dev 2.6.18-194.26.1.el5PAE #1 SMP Tue Nov 9 13:34:42 EST 2010 i686 i686 
i386 GNU/Linux

Which version of Apache?

Server version: Apache/2.2.3
Server built:   Aug 30 2010 12:32:08
Server's Module Magic Number: 20051115:3
Server loaded:  APR 1.2.7, APR-Util 1.2.7
Compiled using: APR 1.2.7, APR-Util 1.2.7
Architecture:   32-bit

Which MPM?

Server MPM:     Prefork
  threaded:     no
    forked:     yes (variable process count)

Please provide any additional information below, especially a URL or an
HTML file that exhibits the problem.

From /var/log/httpd/error_log:

[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/apache/mod_instaweb.cc(247)] ModPagespeed 
OutputFilter called for request /changeset/4610[Mon Nov 15 14:54:46 2010] 
[notice] [1115/145446:INFO:net/instaweb/apache/mod_instaweb.cc(272)] 
unparsed=/changeset/4610, absolute_url=http://trac.davidco.com/changeset/4610
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:1: HtmlParse::StartParse
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/apache/mod_instaweb.cc(299)] Request 
headers:\nHTTP/1.1 0 Internal Server Error\r\nHost: trac.davidco.com
\r\nUser-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; 
rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12\r\nAccept: 
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\nAccept-Langua
ge: en-us,en;q=0.5\r\nAccept-Encoding: gzip,deflate\r\nAccept-Charset: 
ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\nKeep-Alive: 600\r\nConnection: kee
p-alive\r\nReferer: https://trac.davidco.com/ticket/475\r\nCookie: 
__utma=53671997.1988284187.1289234586.1289578563.1289581636.11; 
__utmz=53671997.1289234586.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); 
trac_form_token=c66ebbe9b1629d50d94c186e; 
trac_session=699403b69a5529a41cf0eafa\r\nAuthorization: Basic 
cnBlYWtlOnc4NC5zZzM=\r\n\r\n
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/apache/mod_instaweb.cc(302)] 
request->filename=/var/www/trac/html.wsgi, uri=/changeset/4610[Mon Nov 15 
14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/apache/mod_instaweb.cc(319)] ModPagespeed 
Response headers:\nHTTP/1.1 200 OK\r\nETag: W/"anonymous/Tue, 12 Oct 2010 
16:05:39 GMT/b5e995c78e43112146ef790a25a9958a"\r\nCache-Control: 
must-revalidate\r\nX-Mod-Pagespeed: 0.9.0.0-128\r\n\r\n
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:1: 1701us: HtmlParse::Flush
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:1: 1736us: 
HtmlParse::CoalesceAdjacentCharactersNodes
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:1: 1775us: HtmlParse::ApplyFilter:AddHead
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:126: 1818us: HtmlParse::SanityCheck
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/util/google_message_handler.cc(48)] 
http://trac.davidco.com/changeset/4610:126: 1889us: 
HtmlParse::ApplyFilter:CssCombine
[Mon Nov 15 14:54:46 2010] [notice] 
[1115/145446:INFO:net/instaweb/apache/serf_url_async_fetcher.cc(632)] 
Initiating async fetch for http://trac.davidco.com/chrome/common/css/trac.css