I had some problem connecting to http://www.regione.lombardia.it behind a proxy (squid cache 3.1.20).
The error on client browser is:
The following error was encountered: Read Error
The system returned: (104) Connection reset by peer
To solve this issue change forwarded_for to delete on squid.conf
then reload squid configuration
sudo /usr/sbin/squid3 -k reconfigure