When a ValidationSummary is used on an asp.net page, the MaintainScrollPositionOnPostback property no longer works as expected when one of the validation controls fails. This is because the ValidationSummary calls "window.scrollTo(0,0)" when the page is not valid.

To work around the problem, overwrite the scrollTo function on the page:

<script language="javascript" type="text/javascript">

window.scrollTo = function () { }

</script>

Reference: http://forums.asp.net/t/1157863.aspx