Modal Popup Extender Flash

I'm using the MPE to display a panel that contains a gridview.
It works fine, except that when the page loads (whether it be IE or Mozilla), the panel containing the gridview is visible for a split second and then the MPE hides it. It's kind of confusing to a user - does anybody know how to fix this?

Surround the panel with a div as such:

<div id="divModalPopup" style="display:none"> <asp:Panel ID="pnlModalPopup" runat="server" Height="50px" Width="667px" BackColor="White"><!-- Some content --> </asp:Panel></div>

Thanks,
Chad