title: Two ModalPopupExtenders on a page cause incorrect validation issues
body: <p>I have one aspx page that has two UserControls on it; each is primarily a ModalPopupExtender.  One has validators; one does not.  The one that does not has a Submit button with the CausesValidation="false" attribute on it.</p>
  
  <p>When that Submit button is clicked, nothing happens.  Click it again, and the postback happens as expected.  There is clearly some validation issue going on here, because if I remove all validators from the page, the postback succeeds on the first click.</p>
  
  <p>What's going on here?</p>