Function Doesnt Work Without An Alert()

I have this code in actionscript that calls javascript:

actionscript:

zoom_in = function () {
var tw1:Tween = new Tween(mc_1, "_width", Regular.easeOut,
mc_1._width, 0, 1, false); //OK
var tw2:Tween = new Tween(mc_1, "_height", Regular.easeOut,
mc_1._height, 0, 1, false); //OK
ExternalInterface.call("zoom");
}

javascript:

function zoom()
{
top.resizeTo(1024, 768);
self.moveTo(0,0);
}

Everything works perfectly on Firefox 1.5 but not on IE 6+

in IE the "zoom" function doesn't work, but if I add an alert it DOES work:

function zoom()
{
alert('this works');
top.resizeTo(1024, 768);
self.moveTo(0,0);
}