DropDownExtender

Question

DropDownExtender空间。显示出来的结果只有4个，只显示出了前4个，其他的没显示出来。
如图：
code：
<asp:TextBox ID="txtMz" runat="server" 
                        ontextchanged="txtMz_TextChanged"></asp:TextBox>
                    <asp:Panel ID="Panel1" runat="server" ScrollBars="Vertical" Visible="false" Height="100px">   
                        <asp:GridView ID="GridView1" runat="server" AutoGenerateSelectButton="false"
                            onrowdatabound="GridView1_RowDataBound" 
                            onselectedindexchanged="GridView1_SelectedIndexChanged" 
                            onselectedindexchanging="GridView1_SelectedIndexChanging">
                            <Columns>
                                <asp:BoundField DataField="mz"/>
                            </Columns>
                        </asp:GridView>
                    </asp:Panel>
                <asp:DropDownExtender ID="DropDownExtender1" runat="server" TargetControlID="txtMz" DropDownControlID="Panel1">
                    </asp:DropDownExtender>asp.net