This is due to a security restriction.
I found out that the security restriction is only when the <input type="file"/> is set to display:none; or is visbilty:hidden.
So i tried positioning it outside the viewport by setting position:absolute and top:-100px; and voilà it works.
see http://jsfiddle.net/DSARd/1/
call it a hack.
Hope that works for you.