Because of the way mod_perl handles redirects, the status code is not properly logged. The Apache::RedirectLogFix module works around this bug until mod_perl can deal with this. All you have to do is to enable it in the httpd.conf file.

PerlLogHandler Apache::RedirectLogFix

For example, you will have to use it when doing:

$r->status(304);

and do some manual header sending, like this:

$r->status(304);
$r->send_http_header( );

Available from the mod_perl distribution. See the module manpage for more information.