AJAX Page CallbackPanel - Using XmlDataSource

Callback Panel with DropDownList bind to XmlDataSource.
After panel callback the DropDownList still load.

Items: (bind to XmlDataSource)



ASPX
<oajax:CallbackPanel runat="server" ID="callbackPanel1">
    <content>
        <asp:XmlDataSource ID="XmlDataSource1"
             runat="server"
             DataFile="~/Data/List.xml" />
        <asp:DropDownList ID="DropDownList1"
             runat="server"
             DataSourceID="XmlDataSource1"
             DataTextField="text"
             DataValueField="value" />
        ...


XML - List.xml
<?xml version="1.0" encoding="utf-8" ?>
<data>
    <item value="item1" text="Item 1" />
    <item value="item2" text="Item 2" />
    ...