Proxy .PAC file no longer works

I use a .pac file in order to enable/disable my web proxy when browsing specified sites with Safari. It worked fine under Snow Leopard, but does not work under Lion. My .pac looks like this:

function FindProxyForURL(url, host)

{

// variable strings to return

var proxy_yes = "PROXY my proxy.com:7128";

var proxy_no = "DIRECT";

if (shExpMatch(url, "https://proxy_this_site.com*")) { return proxy_yes; }

if (shExpMatch(url, "http://whatismyipaddress.com")) { return proxy_yes; }

// Proxy anything else

return proxy_no;

}

Any advice on how to get the .pac working again?