title: flex mobile : textInput does not clear prompt on focus
body: <p>a simple </p>
  
  <pre><code>&lt;s:TextInput x="163" y="117"  prompt="hello"/&gt;
  </code></pre>
  
  <p>Does not clear the prompt on focus, but clears the prompt when user first type in a letter.</p>
  
  <p><strong>This is the behaviour on flex mobile</strong> (behaviour is OK on swf )</p>
  
  <p>Is that a bug and how to correct that ?</p>
  
  <p>regards</p>