title: CustomButtonField is not getting selected
body: <p>I am not able select the custombuttonfield</p>
  
  <p>Here is my code:-</p>
  
  <pre><code> public MenuScreen() 
  {
      super(Screen.DEFAULT_CLOSE);
           verticalOffset=Display.getWidth();
           menuBackgroundImage=Bitmap.getBitmapResource("com/greetings/Images/MenuBackground.jpg");
           categories=new CustomSmallButton(Bitmap.getBitmapResource("com/greetings/ButtonImage/categoryon.png"),Bitmap.getBitmapResource("com/greetings/ButtonImage/categoryoff.png"),0);
           categories.setChangeListener(this);
           help=new CustomSmallButton(Bitmap.getBitmapResource("com/greetings/ButtonImage/helpon.png"),Bitmap.getBitmapResource("com/greetings/ButtonImage/helpoff.png"),0);
           help.setChangeListener(this);
           developer=new CustomSmallButton(Bitmap.getBitmapResource("com/greetings/ButtonImage/aboutuson.png"),Bitmap.getBitmapResource("com/greetings/ButtonImage/aboutuspoff.png"),0);
           developer.setChangeListener(this);
  
  
      VerticalFieldManager manager = new VerticalFieldManager()
      {
            protected void sublayout(int width, int height)
        {
                width=fwidth;
                height=fHeight;
                super.sublayout(width,height);
                setPositionChild(categories, width-240, height-350);
                setPositionChild(help, width-240, height-290);
                setPositionChild(developer, width-240, height-230);
                setExtent(width, height);
        }
      };
      manager.setBackground(BackgroundFactory.createBitmapBackground(menuBackgroundImage));
      manager.add(categories);
      manager.add(help);
      manager.add(developer);
      add(manager);
  
  }
  public void fieldChanged(Field field, int context) {
      if(field==categories)
      {
          templateCategories=new TemplateCategories(2);
      UiApplication.getUiApplication().pushScreen(templateCategories);
  
      }
  
      if(field== help)
      {
          helpScreen=new HelpScreen();
          UiApplication.getUiApplication().pushScreen(helpScreen);
      }
  
      if(field == developer)
      {
          developerScreen=new DeveloperScreen();
          UiApplication.getUiApplication().pushScreen(developerScreen);
      }
  
  }
  </code></pre>
  
  <p>when i am clicking help or developer button its not selecting.</p>