title: Up, Down, Left and Right arrow keys do not trigger KeyDown event
body: <p>I am building an application where all the key input must be handled by the windows itself.</p>
  
  <p>I set tabstop to false for each control witch could grab the focus except a panel (but I don't know if it has effect).</p>
  
  <p>I set KeyPreview to true and I am handling the KeyDown event on this form.</p>
  
  <p>My problem is that sometimes the arrow key aren't responsive anymore:</p>
  
  <ul>
  <li><p>The keydown event is not fired when I pressed only an arrow key.</p></li>
  <li><p>The keydown event is fired if I press an arrow key with the control modifier.</p></li>
  </ul>
  
  <p>Have you an idea why my arrow key suddenly stop firing event?</p>