Comment 3 for bug 725635

postinst contains, meaning the current status should be well handled.
  if status squid | grep "start/running" > /dev/null; then
        restart squid
  fi

Oddly, on a lucid server with the recent update, I just tried manually restarting squid with hammering upstart commands and got unexpected resolve. :/

dave@vector:~$ sudo restart squid
restart: Job failed to restart
dave@vector:~$ sudo start squid
squid start/running, process 26242
dave@vector:~$ sudo restart squid
restart: Job failed to restart
dave@vector:~$ sudo start squid
squid start/running, process 26576
dave@vector:~$ sudo restart squid
squid start/running, process 26665
dave@vector:~$ sudo stop squid
squid stop/waiting
dave@vector:~$ sudo restart squid
restart: Unknown instance:
dave@vector:~$ sudo start squid
squid start/running, process 27039
dave@vector:~$ sudo restart squid
squid start/running, process 27085
dave@vector:~$ sudo restart squid
squid start/running, process 27131