JavaScript event window.onload not triggered
I think what's probably happening here is that your window.onload is being overridden later, check to make sure that it's not via things like <body onload="">
You can check this by alert(window.onload) in your re-size function, to see what's actually attached there.
I had this happen when I added 3rd party jQuery code we needed for a partner. I could have easily converted my antiquated window.onload to a jQuery document ready. That said, I wanted to know if there is a modern day, cross browser compatible solution.
There IS!
window.addEventListener ?
window.addEventListener("load",yourFunction,false) :
window.attachEvent && window.attachEvent("onload",yourFunction);
Now that I know ... I can convert my code to use the jQuery route. And, I will ask our partner to refactor their code so they stop affecting sites.
Source where I found the fix --> http://ckon.wordpress.com/2008/07/25/stop-using-windowonload-in-javascript/