一个关于updatepanel的问题，哪位大侠提示下谢谢

<form id="form1" runat="server">
    <div style="height: 650px">
        <asp:ScriptManager ID="ScriptManager1" runat="server">
         </asp:ScriptManager>
           <table border="1" width="600"  bgcolor="#3366FF">
           <tr>
             <td>
             <asp:DropDownList ID="dateselect" runat="server" 
                onselectedindexchanged="dataSelectedIndexChanged" AutoPostBack="true">
                 <asp:ListItem Text="日查询" selected="True" Value="0"/>
                 <asp:ListItem Text="月查询" Selected="false" Value="1"/>
                 <asp:ListItem Text="年查询" Selected="false" Value="2"/>
             </asp:DropDownList>
            </td>
              &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <td>
             <asp:DropDownList ID="typeselect" runat="server"
                onselectedindexchanged="typeSelectedIndexChanged" AutoPostBack="true">
                <asp:Listitem Text="曲线图" Value="0" Selected="True"/>
                <asp:ListItem Text="柱状图" Value="1" Selected="False"/>             
            </asp:DropDownList>
            </td>
          &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;   
             
        
        <asp:UpdatePanel ID="UpdatePanel1" runat="server" RenderMode="Inline">
             <ContentTemplate>      
         <td>
         <asp:Label ID="selectstarttime" runat="server" Font-Bold="True" 
                     Font-Size="X-Small" Text="请选择时间"></asp:Label>
                 &nbsp;<asp:TextBox ID="textbox1" runat="server" Enabled="False" Width="85"></asp:TextBox>
                 <asp:Image ID="Image1" runat="server" src="Images/calendar.gif" onclick="popUpCalendar(this,document.forms[0].textbox1,'yyyy-mm-dd')" />
          </td>      
          </tr>
          <tr align="center">
          <td colspan="3">
        <asp:Button ID="refer" runat="server" Text="提交" onclick="refer_Click" />   
        </td>
          </tr>
        </table> 
             
               
                 <asp:Chart ID="Chart1" runat="server" Height="429px" 
                     ImageLocation="~/WebCharts/f9a710e6-abc4-4169-b5df-6c9df9cb723b.Png" 
                     ImageStorageMode="UseImageLocation" 
                     style="margin-top: 30px; margin-left: 22px;" Width="475px" 
                     BackImageAlignment="Center">
                     <BorderSkin SkinStyle="FrameThin1" BackGradientStyle="None" BorderWidth="0" PageColor="White" BackColor="#CCCCCC" BackImageAlignment="TopLeft">
                     </BorderSkin> 
                     <Series>
                         <asp:Series Name="Low">
                         </asp:Series>
                         <asp:Series ChartArea="ChartArea1" Name="High">
                         </asp:Series>
                         <asp:Series ChartArea="ChartArea1" Name="Middle">
                         </asp:Series>
                          <asp:Series Name="Monitor">
                         </asp:Series>
                     </Series>
                     <ChartAreas>
                         <asp:ChartArea Name="ChartArea1">
                         </asp:ChartArea>
                     </ChartAreas>
                 </asp:Chart>
                 <br />
                 
                 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
                 <asp:Button ID="Up" runat="server" Text="上一页" onclick="Up_Click" />
                 <asp:Button ID="Previous" runat="server" onclick="Previous_Click" 
                     Text="上一个" />
                 
                 <asp:Button ID="Next" runat="server" onclick="Next_Click" Text="下一个" />
                  <asp:Button ID="Down" runat="server" onclick="Down_Click" Text="下一页" />
             </ContentTemplate>
         </asp:UpdatePanel>   
    </div>
    </form>这段页面代码，在第一次初始化时，页面时正常的，当选择条件查询后，那两个下拉列表框就跑到最下面一行去了