HoverMenu with GridView - header disappearing

I have created a gridview control (scrollable) with a hover menu extender (like the one on the sample website). However, when you scroll down the header remains fixed (as it should as I've set it to in Css) until you mouse over any of the records to bring up the hover menu enabled popup panel. When this happens the header disappears completely and the only way to get it back is to scroll back up to the top (where there is now a gap where the header should be) and then mouse over any row. I can't understand why this happens, but it always disappears when you are scrolled further down and then mouse over any row. If you just scroll down and scroll back up to the top without mouse over any of the rows the header stays put as it should.

Here is my code: (by the way this is in the content of an accordion pane which works fine- so I already have AJAX enabled and the SCriptManager present)

<divclass="container"style="height: 370px; Width:auto">

runat="server"

DataKeyNames="CallLookupID"

DataSourceID="srcExistingContacts"

Width="100%"GridLines="None">

<asp:TemplateField>

<HeaderTemplate>

<tablewidth="100%">

<tr>

<tdwidth="30%">Name</td>

<tdwidth="30%">Number</td>

<tdwidth="25%">Group</td>

<tdwidth="15%">Personal?</td>

</tr>

</table>

</HeaderTemplate>

<ItemTemplate>

<asp:PanelCssClass="popupMenu"ID="PopupMenu"runat="server">

<divstyle="border:1px outset white;padding:2px;">

<div><asp:LinkButtonID="lnkEdit"runat="server"CommandName="Edit"Text="Edit"/></div>

<div><asp:LinkButtonID="lnkDelete"runat="server"CommandName="Delete"Text="Delete"/></div>

</div>

</asp:Panel>

<asp:PanelID="Panel9"runat="server">

<tablewidth="100%">

<tr>

<tdwidth="30%"><asp:LabelID="Label1"runat="server"

Text='<%# HttpUtility.HtmlEncode(Convert.ToString(Eval("DestinationName"))) %>'/></td>

<tdwidth="30%"><asp:LabelID="Label2"runat="server"

Text='<%# HttpUtility.HtmlEncode(Convert.ToString(Eval("DestinationNumber"))) %>'/></td>

<tdwidth="25%"><asp:LabelID="Label3"runat="server"

Text='<%# HttpUtility.HtmlEncode(Convert.ToString(Eval("PersonalGroup"))) %>'/></td>

<tdwidth="15%"><asp:CheckBoxEnabled="false"ID="CheckBoxPersonal"runat="server"Checked='<%# Eval("Personal") %>'/></td>

</tr>

</table>

</asp:Panel>

<cc1:HoverMenuExtenderID="hme2"runat="Server"

HoverCssClass="popupHover"

PopupControlID="PopupMenu"

PopupPosition="Left"

TargetControlID="Panel9"

PopDelay="100"/>

</ItemTemplate>

<asp:PanelID="Panel9"runat="server"Width="100%">

<tablewidth="100%">

<tr>

<tdwidth="30%"><asp:TextBoxFont-Bold="true"ID="TextBox1"runat="server"

Text='<%# Bind("DestinationName") %>'/></td>

<tdwidth="30%"><asp:TextBoxID="TextBox2"runat="server"

Text='<%# Bind("DestinationNumber") %>'/></td>

<tdwidth="25%"><asp:TextBoxID="TextBox3"runat="server"

Text='<%# Bind("PersonalGroup") %>'/></td>

Checked='<%# Bind("Personal") %>'/></td>

</tr>

</table>

</asp:Panel>

<cc1:HoverMenuExtenderID="hme1"runat="Server"

TargetControlID="Panel9"

PopupControlID="PopupMenu"

HoverCssClass="popupHover"

PopupPosition="Left"/>

<asp:PanelID="PopupMenu"runat="server"CssClass="popupMenu"Width="80">

<divstyle="border:1px outset white">

<asp:LinkButtonID="lnkUpdate"runat="server"

CausesValidation="True"CommandName="Update"Text="Update"/>

<br/>

<asp:LinkButtonID="lnkCancel"runat="server"

CausesValidation="False"CommandName="Cancel"Text="Cancel"/>

</div>

</asp:Panel>

</EditItemTemplate>

</asp:TemplateField>

</Columns>

</asp:GridView></div>

http://net-ajax.itags.org/q_dotnet-ajax_25102.html