Try setting the If-Last-Modified header in the request to the current time. This should make your proxy get the latest version rather than use a cache version.

The code below uses LWP in debug mode to work through the problem.

#! /usr/bin/perl -w

use strict;
use warnings;

use LWP::Debug qw(+); #for debugging info
use LWP::UserAgent;
use HTTP::Request;
use HTTP::Response;
use HTTP::Date;

# Create a user agent that uses the proxy info from the environment
my $ua = LWP::UserAgent->new(env_proxy=>1);

# Create the request
my $request = HTTP::Request->new('GET'=>'http://www.perlmonks.com/');

# Add the If-Modified-Since header
$request->push_header (if_modified_since=>time2str(time));

#Submit your request
my $response = $ua->request($request); 

if ($response->is_success) {
    print "Retrieved URL OK\n";
}
else {
    print $response->status_line . "\n";
}
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inman