title: Why can't I clear the background property (wpf control)
body: <p>Why does clearing the background using the following method </p>
  
  <pre><code>txb.Background.ClearValue(Control.BackgroundProperty);
  </code></pre>
  
  <p>give an exception of </p>
  
  <blockquote>
    <p>"cannot clear background properties on object '#FFFFFFFF' because it
    is in a read-only state"</p>
  </blockquote>
  
  <p>?</p>