How to implement nested updatepanel

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C#3.5

ASP.NET4

VS2013

I have code

<asp:UpdatePanel runat="server" ID="UpdatePanel1" >
    <ContentTemplate>
        <asp:Panel ID="pnlSearchNow" runat="server">
<div class="row clearfix">
                <div class="col-md-5">
                    <asp:UpdatePanel runat="server" ID="updchkListMY">
                        <ContentTemplate>
                           <asp:DropDownList runat="server" ID="id1" OnSelectedIndexChanged="id1_SelectedIndexChanged"></asp:DropDownList> 
                        </ContentTemplate>
                    </asp:UpdatePanel>
                </div>
                <div class="col-md-5">                            
                    <asp:UpdatePanel runat="server" ID="updchkListGodown">
                        <ContentTemplate>
                            <asp:DropDownList runat="server" ID="id2" OnSelectedIndexChanged="id2_SelectedIndexChanged">
</asp:DropDownList>                                 </ContentTemplate>
                    </asp:UpdatePanel>
                </div>
            </div>
            <div class="row clearfix">
                <div class="col-md-12">
                    <div class="box">
                        <div class="box-body">
                            <asp:UpdatePanel runat="server">
                                <ContentTemplate>                                            
                                    <div class="row clearfix">
                                        <div class="col-md-12">                                                                                <asp:GridView ID="gvPayment" runat="server" AutoGenerateColumns="false" ShowFooter="true"  Width="100%" >
</asp:GridView>
</div>                    </div>
</ContentTemplate>
</asp:UpdatePanel>
<div class="row clearfix"> <div class="col-md-2">  <asp:UpdatePanel runat="server">                                                <ContentTemplate>
                                            <div class="col-md-2">
                                                <asp:DropDownList runat="server" ID="ddlBankName" AutoPostBack="true" CssClass="form-control input-sm" OnSelectedIndexChanged="ddlBankName_SelectedIndexChanged"></asp:DropDownList>
                                            </div>
                                            <div class="col-md-2">
                                                <asp:DropDownList runat="server" ID="ddlBranchName" CssClass="form-control input-sm" placeholder="Select Branch"></asp:DropDownList>                                                    </div>
                                        </ContentTemplate>                                       
                                    </asp:UpdatePanel>
</div>
            </div>
                </div>
            </div>
                </div>
            </div>
</asp:Panel>
    </ContentTemplate>
</asp:UpdatePanel>

GridView Bind at id1_SelectedIndexChanged and id2_SelectedIndexChanged and I Calculate some textboxes in GridView.
but when OnSelectedIndexChanged="ddlBankName_SelectedIndexChanged" is fire my calculation on gridview is removed