dropdown in user control not firing first time

 
hi all
i have created some user controls and loading that controls dynamically it's working fine with help of one placeholder. In one of my user control having some dropdown and text box controls . When i select the dropdown in user control then the index changed event is not firing first time but second time itself firing. I don't know why the user control dropdown is not firing in first time. Please do the needful help
parentpage.aspx :
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
            <ContentTemplate>
                <asp:PlaceHolder ID="phmaincontent1" runat="server"></asp:PlaceHolder>
            </ContentTemplate ...