title: WPF validation - ValidatesOnTargetUpdated
body: <p>I have a number of textboxes in a WPF app on which I have set up some validation.</p>
  
  <p>On load the app deserialises a class onto which the WPF window's controls are bound.</p>
  
  <p>I have a ValidationRule that (for example) tests that a file exists.  If I don't set ValidatesOnTargetUpdated then the corresponding TextBox validates when I change the (bound) Text Property and I see the (default) red border appear and a Tooltip (<code>{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors).CurrentItem.ErrorContent}</code>) displaying the error message.</p>
  
  <p>I want the controls to validate on binding rather than on propertychanged so I have set the ValidatesOnTargetUpdated to true and can see the validationRule firing when debugging.</p>
  
  <p>My problem is that the (default) ValidationTemplate is ignored when <code>ValidatesOnTargetUpdated="True"</code> despite the ValidationRule firing.</p>
  
  <p>I can see the Tooltip - it appears with the correct error message but the border doesn't show as Red; this seems to be ignored.</p>
  
  <p>Any ideas why this would be happening?</p>