title: HeadsUp Notification not displayed on KitKat
body: <p>I have a notification, presented using the following code:</p>
  
  <pre><code>    // Create the notification
      android.app.Notification systemNotification = new NotificationCompat.Builder(context)
              // Set notification data and appearance
              .setContentTitle(notification.getNotificationLabel())
              .setContentText(notification.getMessage())
              .setSmallIcon(notification.getNotificationDrawable())
              .setWhen(new Date().getTime())
  
              // Set notification options
              .setCategory(NotificationCompat.CATEGORY_MESSAGE)
              .setPriority(NotificationCompat.PRIORITY_HIGH)
              .setDefaults(NotificationCompat.DEFAULT_ALL)
              .build()
      ;
  
      NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
  
      notificationManager.notify(notification.getNotificationId(), systemNotification);
  </code></pre>
  
  <p>When run on Lollypop and newer, it works fine and the notification appears both in the status bar and as a popup notification as expected/desired.  On Kitkat, the notification only appears in the status bar, there's no popup notification.  I can still open the notification from the status bar and everything looks and works fine, it's just the popup notification that's missing.</p>
  
  <p>Some of the things I've tried so far:</p>
  
  <ul>
  <li>different options to <code>setDefaults</code></li>
  <li>different options to <code>setPriority</code></li>
  <li>verified that notifications are on in the system settings panel for the application</li>
  </ul>