If I hide and then show the two DatePickers then the artifact disappears.
I downloaded and included the latest JQuery in my project.
<script src="JQuery/jquery-1.4.2.min.js" type="text/javascript"></script>
<script src="JQuery/jquery-ui-1.8.1.custom.min.js" type="text/javascript"></script>
<link href="JQuery/jquery.ui.all.css" media="screen" rel="stylesheet" type="text/css"/>
I've attached a screenshot of a section of the web page with the datepickers and the artifact.