title: JavaFX 2 ComboBox setValue() does not set CB text
body: <p>My problem is that the selected ComboBox item text is not visible on the screen after selecting it with setValue().
  Here are some details:
  Adding items to my CB:</p>
  
  <pre><code>combo.getItems().add("a");
  combo.getItems().add("b");
  combo.getItems().add("c");
  combo.getItems().add("d");
  </code></pre>
  
  <p>Afterwards, when Button A is pushed:</p>
  
  <pre><code>combo.setValue(null);
  </code></pre>
  
  <p>When Button B is pushed:</p>
  
  <pre><code>combo.setValue("a");
  </code></pre>
  
  <p>Now, if I push Button B first, "a" is shown, thats OK.
  After that if I push Button A, no text is shown on the ComboBox, thats OK.
  Then I push B, and the value did not change on the screen. However, if I click on the CB, the row for "a" is highlighted, and combo.getValue() returns "a".</p>
  
  <p>Any suggestions how to handle this?</p>