This may be a bug in internet explorer (IE9), wondering if it is known or there is a workaround.
It can be reproduced by opening up the dev console, and executing each of these commands,
window.onresize = function() { alert("onresize"); }
At this point, when you resize the window, the event fires as expected. Now execute,
document.write("test"); 
After this point window.resize will be null. 
That's probably expected since document.write calls document.open which clears everything.
However, even if you add back an event handler, it will never fire,
window.onresize = function() { alert("onresize"); } 
 
    