I changed the configuration file /etc/squid-deb-proxy/squid-deb-proxy.conf like this:
# and only to ubuntu -http_access deny !to_ubuntu_mirrors +#http_access deny !to_ubuntu_mirrors +cache deny !to_ubuntu_mirrors +http_access allow !to_ubuntu_mirrors
It seems to be the expected behavior.
I changed the configuration file /etc/squid- deb-proxy/ squid-deb- proxy.conf like this:
# and only to ubuntu
-http_access deny !to_ubuntu_mirrors
+#http_access deny !to_ubuntu_mirrors
+cache deny !to_ubuntu_mirrors
+http_access allow !to_ubuntu_mirrors
It seems to be the expected behavior.