按钮单击事件未在弹出扩展器内触发

Question

我有popupextender。当我点击popupextender中的按钮时，第一次没有触发。

示例：

<asp:Image ID="imgDown" ImageUrl="../Images/arrow_down1.gif" runat="server" />
<asp:Panel ID="pnlInboxResumes" runat="server" 
           Width="35px" 
           BorderColor="#99CCFF" 
           BorderStyle="Solid" 
           BorderWidth="1" 
           BackColor="White" 
           Style="display: none;">
    <table border="0" align="left" cellpadding="3" cellspacing="0">
        <tr>    
            <td>
                <asp:DataList 
                        ID="dlInboxResumes" 
                        runat="server" 
                        OnItemCommand="dlInboxResumes_ItemCommand" 
                        OnItemDataBound="dlInboxResumes_ItemDataBound" 
                        on RepeatDirection="Vertical" 
                        DataKeyField="Path">
                    <ItemTemplate>
                        <asp:ImageButton 
                                ID="imgbtnResume" 
                                runat="server" 
                                ImageUrl="~/Images/ParseResume_3.png" 
                                CausesValidation="false" 
                                CommandName="select" 
                                EnableViewState="true"/>
                    </ItemTemplate>
                </asp:DataList>
            </td>
        </tr>
    </table>
</asp:Panel>
<asp:PopupControlExtender 
        ID="InboxParseResumes" 
        runat="server" 
        TargetControlID="imgDown" 
        PopupControlID="pnlInboxResumes" 
        Position="Bottom" 
        CommitProperty="ImageUrl">
</asp:PopupControlExtender>