title: QListWidget does not emit a signal itemEntered(QListWidgetItem*)
body: <p>In my program, QListWidget be used in more than three place. Only one place, QListWidget does not emit the signal itemEntered(QListWidgetItem*).</p>
  
  <p>My code:</p>
  
  <pre><code>MyListWidget::MyListWidget(QWidget* parent):QListWidget(parent)
  {
      this-&gt;setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
      this-&gt;setMouseTracking(true); 
      connect(this, SIGNAL(itemEntered(QListWidgetItem*)),        
              this, SLOT(slotOnItemEntered(QListWidgetItem*)));
  }
  MyListWidget::slotOnItemEntered(QListWidgetItem* item)
  {
      // do something
  }
  </code></pre>
  
  <p>When I debug, and move mouse glide the item, the program cannot go in the slotOnItemEntered(...) function.
  I want to konw, what condition can cause this phenomenon.</p>