iframes always leak in IE?!

<!doctype html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title>iframes always leak in IE?!</title>
</head>
<body>

<p><button id="create">Create iframe</button></p>

<p><button id="remove">Remove iframe</button></p>

<p><button id="garbage">CollectGarbage()</button></p>

<script>

function addEvent(element, evt, callback) {
    if (element.attachEvent) {
        element.attachEvent('on' + evt, callback);
    } else {
        element.addEventListener(evt, callback, false);
    }
}

addEvent(document.getElementById('create'), 'click', function(){
    var iframe = document.createElement('iframe');
    iframe.src = 'http://en.wikipedia.org/wiki/Memory_leak';
    document.body.appendChild(iframe);
    iframe = null;
});

addEvent(document.getElementById('remove'), 'click', function(){
    var iframe = document.getElementsByTagName('iframe')[0];
    iframe.src = 'about:blank';
    document.body.removeChild(iframe);
    iframe = null;
});

addEvent(document.getElementById('garbage'), 'click', function(){
    if (window.CollectGarbage) { window.CollectGarbage(); }
});

</script>

</body>
</html>