MooTools animation bug with % on the stylesheet

by gonchuki

HTML

<div class="box"></div>

CSS

body, html {
    height: 100%;
}

body {
    background: #69a url('http://jsfiddle.net/img/logo.png') no-repeat 100% 100%;
}

.box {
    background-color: #a83;
    position: absolute;
    top: 20%;
    right: 0;
    width: 80px;
    height: 80px;
}

JavaScript

window.addEvent('domready', function(){
    $(document.body).morph.delay(1000, $(document.body), {'background-position':'10px 100px'});
    document.getElement('.box').morph.delay(2000, document.getElement('.box'), {'right':'100px', 'top': '20%'});
});