title: WPF: Validation.ErrorTemplate not hidden when adorned control (TextBox) hidden
body: <p>I have a TextBox that gets hidden depending on whether an item is selected in a ComboBox. </p>
  
  <p>This part works fine.</p>
  
  <p>However, it also has ValidatesOnDataErrors set and if the TextBox has an error present, then when the TextBox gets hidden, the ErrorTemplate (in the Adorner layer) remains.</p>
  
  <p>I think I understand that because the ErrorTemplate gets set into the global Adorner layer, it doesn't realize that the TextBlock, which it has no logical connection to, has been hidden.</p>
  
  <p>Any thoughts on how to work with or around this? I've tried adding an explicit AdornerDecorator inside a Grid, which is bound to the ComboBox value.</p>