Custom validator does not work when in presence of other validators

I have been trying to get a custom validator to work to no avail. So I stripped it out of my page and placed it on a simpler test page with just a submit button and viola! it works. (For testing the codebehind has it hardwired to fail). However I found that if I add another control with a required field validator, it will fail. If I leave the control but comment out the required field validator, it will work again. You can test it yourself. Here is my code.
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"> <asp:ValidationSummary ID="ValidationSummary1" runat="server" CssClass="ValidationSummary" /> <asp:CustomValidator ID="Q1_CustomValidator" runat="server" ErrorMessage="Q1 Fails" Text="*" CssClass="validator" Display="Dynamic" EnableClientScript= ...