selectedIndexChanged of gridview inside updatepanel still refresh all of the page

Hi,
 I have a gridview1 and formview1 and gridview2 inside an updatePanel and other controls. The updatemode is conditional and childrenAsTriggers is set to true
on the updatePanel1. The gridview1 has selected buttons (in a commandField).On clicking the link button inside the grid view
will show the detail in formivew1(master) and gridview2(detail). My question is the form still Causes Full Postback.
How can I avoid this.The following is the code-
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"
                    RenderMode="Inline" ChildrenAsTriggers="False">
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="GridView1"
                            EventName="SelectedIndexChanged"  />
                    </Triggers>
                    <ContentTemplate>
...
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True"
                                                    EnableSortingAndPagingCallbacks="true" AutoGenerateColumns="False" CellPadding="4"
                                                    DataKeyNames="voucherno" ForeColor="#333333" GridLines="None" Height="1px" PageSize="12"
                                                    Width="100%" Font-Size="17px" UseAccessibleHeader="False">
                                                    <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
                                                      <Columns>
                                                        <asp:TemplateField ShowHeader="False">
                                                            <ItemTemplate>
                                                                <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Select"
                                                                    Font-Size="13px" Text="selected"></asp:LinkButton><asp:Label ID="lbTest" runat="server"
                                                                        Text='Eval("Test")%>' Visible="False"></asp:Label>
                                                            </ItemTemplate>
                                                            <ControlStyle Width="100%" />
                                                            <ItemStyle Width="70px" />
                                                        </asp:TemplateField>

Thanks.