To keep the AJAX UpdatePanel in ASP.NET from changing scroll position (and causing a snap-to effect) insert this Javascript function beneath the ScriptManager tag.

<script type="text/javascript">
//This code keeps the AJAX postback from affecting scroll position.
var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_beginRequest(beginRequest);

function beginRequest() {
   prm._scrollPosition = null;
}
</script>