Unfortunately it seems deeper than that.

Looking at the code over on github here, you can see that the ->new method checks if mod_perl is being used and, if it is, gives you back an object with the request attached to it, and all that stuff...

But, regardless, I dumbed down the script to just...

#!/perl/bin/perl

use strict;
use warnings;

use Data::Dumper::Names;
use CGI;

use Apache2::Connection ();
use Apache2::RequestRec ();


$| = 1;

my $header = CGI::header();

print STDERR Dumper($header);
[download]

...and it still outputs just...

$header = '';
[download]