VS2012 ModaPopupExtender CancelControl And OkControl Triggering Validation

I've got an UpdatePanel nested in a Panel control. I'm using a ModalPopupExtender to "popup" the UpdatePanel which provides a list control that a user can select from, which places the selected item in a textbox. This part works fine, but if I select items and click on the CancelControl or OkControl each control is triggering validation on some of the other controls on the page and not triggering the click event. I'm not using validation at this point, but put all the other controls in a validationgroup, but it didn't work. If I don't select any listbox items and click on the CancelControl or OkControl, they behave as expected. Here is a sample of what my panels generally look like:

Code:
<asp:Panel ID="Panel" runat="server" >
<div>
<asp:Button ID="btnStuff" CssClass="button" runat="server" Text="Stuff" OnClientClick="doStuff" />
<asp:Button ID="btnMoreStuff" CssClass="button" runat="server" Text="MoreStuff"

[Code].....