Hello,
I am not 100% sure, but I think the problem you report is similar to the one discussed in this forum thread:
http://forums.infragistics.com/forums/t/11738.aspx
A possible solution you may try is to run the following javascript in the grid client side InitializeLayoutHandler event
<ClientSideEvents InitializeLayoutHandler="UltraWebGrid_InitializeLayoutHandler" />
to the displaylayout section with the following JS
<script type="text/javascript" >
function UltraWebGrid_InitializeLayoutHandler(gridName)
{
var grid = igtbl_getGridById(gridName);
var div = grid.getDivElement();
div.style.position="relative";
}
</script>
Hope this helps.