ModalPopupExtender is not perfect, or it's my mistake?

Hi

I'm using the ModalPopupExtender on my website http://cheirabem.com and it's ok but there are some issues. My modal is connected to gridview I don't use panel because I need to make it responsive. Here is my code:

<!-- inicio das coisas do shipping costs --><asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager><ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" BackgroundCssClass="modalBackground" PopupControlID="Gridview1" TargetControlID="HyperLink1" ></ajaxToolkit:ModalPopupExtender>                                                   <asp:GridView ID="GridView1" CssClass="table table-hover table-striped pnlBackGround" GridLines="None"  runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1"><Columns><asp:TemplateField SortExpression="bandeira"><EditItemTemplate><asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("bandeira") %>'></asp:TextBox></EditItemTemplate><ItemTemplate><asp:Image ID="Image12" runat="server" Height="71px" ImageUrl='<%# Eval("bandeira") %>' Width="63px"  /></ItemTemplate></asp:TemplateField><asp:BoundField DataField="paises" HeaderText="Country" SortExpression="paises"><ItemStyle Font-Size="X-Small" /></asp:BoundField><asp:BoundField DataField="tipo" HeaderText="Service" SortExpression="tipo" ><ItemStyle Font-Size="XX-Small" /></asp:BoundField><asp:BoundField DataField="preco" HeaderText="Price" SortExpression="preco" DataFormatString="{0:c}" ><ItemStyle Font-Bold="True" ForeColor="Red" Font-Size="X-Small" /></asp:BoundField><asp:TemplateField ShowHeader="False"><ItemTemplate><asp:Button ID="Button1" runat="server" CausesValidation="false" CommandName="" OnClick="Button1_Click" Text="Close" /></ItemTemplate></asp:TemplateField></Columns></asp:GridView><asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:produtos %>" ProviderName="<%$ ConnectionStrings:produtos.ProviderName %>" SelectCommand="select * from shipping order by id"></asp:SqlDataSource>                                                  <!-- fim das coisas do shipping costs -->

First when I come to adrress I see the gridview (You can check it http://cheirabem.com option Shipping costs (Europe)) and when I hit the close button I see it again.

Any help to make it better?

Regards