Gridview redirect button and back button problem

My problem. I have an GridView inside an updatePanel. When I click in a button inside the gridview it redirects to another page. But when I click in back button in browser gets to the same page as before but with Session["Id"] changed. And it does PageLoad when I click at any item inside the page. It there's a way if I click back button that or redirect to first page or give me the same page as before with the same Sessions and not enter PageLoad??   thanks

//My ScriptManager
<asp:ScriptManager ID="ScriptManager1" runat="server" EnableHistory="true" EnableSecureHistoryState="false"
        EnablePartialRendering="true" OnNavigate="ScriptManager1_Navigate">
    </asp:ScriptManager>


//My update panel:
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always">

//My gridView:

 <asp:GridView ID="grid" runat="server" EnableModelValidation="true" AutoGenerateColumns="false"
                AllowPaging="true" PageSize="20" Width="100%" Font-Size="Smaller" OnRowDataBound="grid_RowDataBound"
                OnPageIndexChanging="grid_PageIndexChanging" 
                OnRowCommand="grid_RowCommand">
                <HeaderStyle ForeColor="White" />
                <Columns>
                    <asp:BoundField HeaderText="Name" DataField="name">
                        <ItemStyle />
                    </asp:BoundField>
                    <asp:BoundField HeaderText="id" DataField="id">
                        <ItemStyle />
                    </asp:BoundField>
                    <asp:BoundField HeaderText="AnotherField" DataField="anotherField">
                        <ItemStyle />
                    </asp:BoundField>
                    <asp:BoundField HeaderText="AnotherField2" DataField="anotherField">
                        <ItemStyle />
                    </asp:BoundField>
                    <asp:TemplateField>
                        <ItemTemplate>
                            <asp:ImageButton ID="btnRedirect" runat="server" CommandArgument='<%#DataBinder.Eval(Container.DataItem,"id") %>' CommandName="redirect"
                                ToolTip="Redirect" />
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>




//My Code Behind:

 protected void ScriptManager1_Navigate(object sender, HistoryEventArgs e) // Event handler for restoring state
        {
          Session["Id"] = e.State["value"]; 
        }

protected void grid_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            string id= Convert.ToString(e.CommandArgument);
            if (e.CommandName == "redirect")
            {

                ScriptManager.GetCurrent(Page).AddHistoryPoint("value", idInThePage); 
                Session["TipoDocumento"] = id;
                Response.Redirect("RedirectPage.aspx");
            }
        }