Firefox + "overflow-y:scroll;" is vertical calculation bug?

Firefox + "overflow-y:scroll;" is vertical calculation bug?


"overflow-y:scroll;" is used with Style Sheet.
When the object that specifies draggable() with the page scrolled is
moved, the calculation of the length position becomes amusing.
details environment:
Firefox 3.0.11
jQuery 1.3.2
jQery UI 1.7.2
sample HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://
www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="ja" lang="ja"
dir="ltr">
<head>
<meta http-equiv="Content-Language" content="ja" />
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta http-equiv="Content-Style-Type" content="text/css;
charset=UTF-8" />
<meta http-equiv="Content-Script-Type" content="text/javascript;
charset=UTF-8" />
<style type="text/css">
html {
    overflow-y:scroll;
}
</style>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/
libs/jquery/1.3.2/jquery.min.js"></script>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/
libs/jqueryui/1.7.2/jquery-ui.min.js"></script>
<script type="text/javascript">
$(function() {
    $(".Gadget").draggable();
});
</script>
<title>jQuery UI bug?</title>
</head>
<body>
<span class="Gadget">string</span>
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
</body>
</html>