I'm having problems trying to get a mod_perl handler (a modified version of Lincoln Stein's Apache::NavBar) to filter the output of a CGI script (setup via Apache::OutputChain).

I've narrowed down the problem to something this simple:

Here's the CGI script:

#!/usr/local/bin/perl

use strict;
use CGI qw/:standard/;

print header();
print start_html();
print "hello world\n";
print end_html;
[download]

Here's the relevant part of my httpd.conf:

<Location /perl>
  SetHandler perl-script
  PerlHandler Apache::OutputChain Apache::NavBar Apache::Registry
  Options +ExecCGI
</Location>
[download]

And the snippet that is causing me the problem in Apache::NavBar:

sub handler {
  my $r = shift;
  warn "OK handler\n";
  warn "CT: ", $r->content_type, "\n";
  $r->content_type eq 'text/html' || return DECLINED;
  warn "OK text/html\n";
[download]

Whenever I invoke the CGI script, I get this in the output log: OK handler
CT:

That's right. The call to $r->content_type produces no output, even though it's set by default in the CGI script. I've tried forcing the issue:

print header(-type=>"text/html");
[download]

I even tried using bare print statements in case CGI.pm was doing something strange but I keep getting the same results. My guts tell me that I'm either missing something very fundamental in my understanding of the API or that something fishy is happening in mod_perl/Apache::Registry/Apache:OutputChain.

Some more information:
Red Hat 6.2 with all updates applied. If y'all want/need specific versions I can dig them up.

Thanks for your help,
Colin Kuskie