MaintainScrollPositionOnPostback not working with javascript:__doPostBack

Put the grid inside a panel (rather than scrolling the grid itself) and the following in the head section of the page. This is set for using a MasterPage, but you can remove the "ctl00_MainContentPlaceHolder_" prefix for a regular page.

<script type="text/javascript" language="javascript">
        window.onload = function () {
                var strCook = document.cookie;

                if (strCook.indexOf("!~") != 0) {
                        var intS = strCook.indexOf("!~");
                        var intE = strCook.indexOf("~!");
                        var strPos = strCook.substring(intS + 2, intE);
                        document.getElementById("ctl00_MainContentPlaceHolder_pnlFindings").scrollTop = strPos;
                }

        }
</script>
<script type="text/javascript" language="javascript">
        function SetDivPosition() {
                var intY = document.getElementById("ctl00_MainContentPlaceHolder_pnlFindings").scrollTop;
                document.cookie = "yPos=!~" + intY + "~!";
        }
</script>

In the Panel, you'll need:
onscroll="SetDivPosition()"

That should do it for you. Works for me, anyway.