how i an updatepanel prevent compositecontrol's dropdownlist

i have compositecontrol contains dropdownlist.

i have set autopostback ability dropdownlist true.

on page, i have:

<asp:updatepanel id="updatepanel" runat="server">
    <contenttemplate>
        <mycontrol:control id="customcontrol" runat="server" />
    </contenttemplate>
</asp:updatepanel>

i've also attempted sourroundings childrenastriggers="true" updatemode="always," nonetheless conjunction resolved problem.

the problem updatepanel intercepting compositecontrol's dropdownlist's post back. (a full post being achieved dropdownlist changed)

how i updatepanel hoop postback?

thanks!

edit -- requested info

country states both dropdownlists compositecontrol.

country.selectedindexchanged += new eventhandler(country_selectedindexchanged);

protected vacant country_selectedindexchanged(object sender, eventargs e)
{
    states.datasource = xxx;
    states.databind();
}