Curvey Corners Not Working With UpdatePanel On IE

I am loading the calendar inside the update panel. when the page loads, the calendar renders the day events for current month.

Curvery corners works fine on Firefox, Chrome and Safari even after the page load but not on IE.
here is the code:

<script type="text/javascript">
Sys.Application.add_load(AppLoad);
function AppLoad() {
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequest);
//Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequest);
}
function pageLoad() {
var isAsyncPostback = Sys.WebForms.PageRequestManager.getInstance().get_isInAsyncPostBack();
if (isAsyncPostback) {
tb_init("a.thickbox, area.thickbox, input.thickbox");
}
else {
var btn = document.getElementById("ctl00_contentBody_BtnReload");
if (btn) {
btn.click();
}
}
}
function loadCalendar() {
__doPostBack('ctl00_contentBody_UPCalendar', '');
}
</script>