setOnlineURL() causes IE9 to be forever offline

[jabbett]

Everything works fine in all browsers if I use the default settings, but when I set a custom URL, Internet Explorer 9 "goes offline."

I created a simple JSFiddle to test this: http://jsfiddle.net/j9v1owwf/4/

And here's a screenshot showing the Fiddle running, making successful requests, but only my offline handler gets called.