JQuery - Dialog Jquery se cierra al hacer postback en asp.net

$(document).ready(function () {

            $('#dialog').dialog({

                autoOpen: false,

                width: 800,

                buttons: {},

                open: function (type, data) {

                    $(this).parent().appendTo("form:first");

                }

            });

            $("#asd1").click(function () {

                jQuery('#dialog').dialog('open');

            });

        });

<div id="dialog">

                <asp:Label ID="lblNewName" runat="server" Text="Name"></asp:Label>

                <asp:TextBox ID="txtNewName" runat="server"></asp:TextBox>

                <asp:DropDownList ID="DropDownList1" runat="server"  AutoPostBack="true"

                    onselectedindexchanged="DropDownList1_SelectedIndexChanged" >

                    <asp:ListItem Text="1" Value="1"></asp:ListItem>

                    <asp:ListItem Text="2" Value="2"></asp:ListItem>

                    <asp:ListItem Text="3" Value="3"></asp:ListItem>

                </asp:DropDownList>

                <asp:Button ID="btnAddSave" runat="server" Text="Save" onclick="btnAddSave_Click" />

</div>