CompareValidator响应似乎错误/不正确？

Question

据我所知，如果我先选择开始日期[左栏]，我会看到开始日期CompareValidator。但是，如果我选择结束日期优先[右栏]，而开始日期为空，我不会得到CompareValidator。

最重要的是，如果我选择先启动[get CompareValidator错误]，然后选择无效的结束日期[小于开始]，我将失去CompareValidator错误

我有什么遗失的吗？

<asp:GridView ID="dg" style="min-width:600px !important;" class="panel-primary" runat="server" GridLines="Vertical" BorderStyle="Solid" BorderColor="#097CAF" ShowFooter="false" AutoGenerateColumns="false" CellPadding="3" OnEditCommand="dg_Edit" OnCancelCommand="dg_Cancel" OnUpdateCommand="dg_Update" DataKeyField="DUMMYVALUE" onrowcommand ="DUMMYVALUE">
          <HeaderStyle Font-Names="Arial" Font-Size="12pt"  HorizontalAlign="Center" Font-Bold="true" BackColor="#097CAF" ForeColor="#FFFFFF" cssClass="headerPad"/>
          <RowStyle Font-Names="Arial" Font-Size="12pt" HorizontalAlign="Left" BackColor="White" />
          <AlternatingRowStyle  Font-Names="Arial" BackColor="#F7F7F7" />   
              <Columns>

                   ------------------
                 <asp:TemplateField HeaderText="<p style='padding-top:10px;padding-left:10px;'>Start Date</p>" ItemStyle-Width="150" >

                   <ItemTemplate>
                       <div style="padding-left:10px;padding-right:10px;padding-bottom:5px;padding-top:5px;">
                                                                            <asp:Textbox ID="lblStart" Text='<%#Container.DataItem("StartDate")%>' runat="server" cursor="default" BackColor="transparent" class="form-control"/>

                          <ajaxToolkit:CalendarExtender ID="calcdgStart" runat="server" TargetControlID="lblStart" OnClientDateSelectionChanged="detect_weekend" />

                              <asp:CompareValidator ID="cvStartGreater" ControlToValidate="lblStart" Operator="LessThanEqual" Display="Dynamic" ControlToCompare="lblEnd" OnServerValidate="validateTheTextBox_OnServerValidate" ErrorMessage="Must be less than End Date" runat="server" style="color:red;"/>   
                      </div> 
                   </ItemTemplate>

               </asp:TemplateField>

               <asp:TemplateField HeaderText="<p style='padding-top:10px;padding-left:10px;'>End Date</p>" ItemStyle-Width="150">

                  <ItemTemplate>
                     <div style="padding-left:10px;padding-right:10px;padding-bottom:5px;padding-top:5px;">

                        <asp:Textbox ID="lblEnd" Text='<%#Container.DataItem("EndDate")%>' runat="server" cursor="default" BackColor="transparent" class="form-control"/>

                        <ajaxToolkit:CalendarExtender ID="calcdgEnd" runat="server" TargetControlID="lblEnd"  OnClientDateSelectionChanged="detect_weekend" />

                        <asp:CompareValidator ID="cvEndGreater" ControlToValidate="lblEnd" Operator="GreaterThanEqual" Display="Dynamic" ControlToCompare="lblStart" OnServerValidate="validateTheTextBox_OnServerValidate" ErrorMessage="Must be greater than Start Date" runat="server" style="color:red;"/> 
                    </div>                                                      
                  </ItemTemplate>

               </asp:TemplateField>

          ----------------------------                                                  
            </Columns>
</asp:GridView>