Buggy jQueryUI slide

This example show when the slide is bugging out

HTML

<script src="http://www.azatoth.net:8080/~azatoth/jquery-ui-1.8rc3/ui/jquery-ui.js"></script>
<button>Click</button>
<div class="obj1">
<div class="obj2">Hello World</div>
</div>

CSS

.obj1 {
height: 2000px;
width: 100%;
}

.obj2 {
width: 50%;
height: 100px;
background: red;
border: 3px dashed green;
}

JavaScript

$("button").click(function(){$(".obj2").hide("slide", {}, 2000).show("slide")});