swing toolBar中按钮形状问题

Question

环境：myeclipse10 windowsXP jdk1.7 jre7问题：如上图，第一个按钮形状不正常，不应该是鼓起来的。这种现像仅是在WindowsLookAndFeel风格下才有。代码中我对每个JButton都执行了：
setFocusPainted(false);
setSelected(false);请问是什么原因？附全部代码：package jNote;public class Main {
public static void main(String[] args)
{
Window wnd = new Window();
wnd.setVisible(true);
}
}
package jNote;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class Window extends JFrame{

public Window()
{
  this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);// 设置关闭动作
  this.setSize(800, 600);// 设置窗口大小
  this.setTitle("JNote"); //设置标题
  this.setLocationRelativeTo(null);// 使窗口显示在屏幕中央
  //this.setExtendedState(JFrame.MAXIMIZED_BOTH);//初始窗口最大化
  
  try{
  enableEvents(AWTEvent.WINDOW_EVENT_MASK);
  }
  catch(Exception e){}
  
      ImageIcon imgIcon = new ImageIcon(this.getClass().getResource("images/jNote_16.png"));
      Image img = imgIcon.getImage();
      this.setIconImage(img);
  
  JToolBar tb = new JToolBar();
  tb.setPreferredSize(new Dimension(800,30));
  tb.setFloatable(false);//是否可拖动
  
          JButton bt_new = new JButton();
          bt_new.setPreferredSize(new Dimension(20,20));
          bt_new.setOpaque(false);
          bt_new.setFocusPainted(false);
          bt_new.setIcon(new ImageIcon(this.getClass().getResource("images/new.png")));
          bt_new.setToolTipText("新建");
          bt_new.setBorderPainted(false);
          bt_new.setSelected(false);
  //tb.addSeparator();
          
          JButton bt_open = new JButton();
          bt_open.setPreferredSize(new Dimension(20,20));
          bt_open.setOpaque(false);
          bt_open.setFocusPainted(false);
          bt_open.setIcon(new ImageIcon(this.getClass().getResource("images/open.png")));
          bt_open.setToolTipText("打开");
          bt_open.setBorderPainted(false);
          bt_open.setSelected(false);
          
          JButton bt_save = new JButton();
          bt_save.setPreferredSize(new Dimension(20,20));
          bt_save.setOpaque(false);
          bt_save.setFocusPainted(false);
          bt_save.setIcon(new ImageIcon(this.getClass().getResource("images/save.png")));
          bt_save.setToolTipText("保存");
          bt_save.setBorderPainted(false);
          bt_save.setSelected(false);
          
          bt_new.addActionListener(new NewHandler());
          
          tb.add(bt_new);
          tb.add(bt_open);
          tb.add(bt_save);   this.getContentPane().add(tb,BorderLayout.NORTH);
  //设置swing窗口系统风格
  //String look = "com.sun.java.swing.plaf.windows.WindowsLookAndFeel";
  //String look = "com.sun.java.swing.plaf.windows.WindowsLookAndFeel";
  //String look = "com.sun.java.swing.plaf.motif.MotifLookAndFeel";
  //String look = "com.sun.java.swing.plaf.mac.MacLookAndFeel";
  String look = "com.sun.java.swing.plaf.gtk.GTKLookAndFeel";
  try
  {
   UIManager.setLookAndFeel(look);
   SwingUtilities.updateComponentTreeUI(this);
  }
  catch(Exception ex)
  {}
}

protected void processWindowEvent(WindowEvent e) {
boolean enable = false;
if (e.getID() == WindowEvent.WINDOW_CLOSING) {
//处理Jframe关闭事件
int option= JOptionPane.showConfirmDialog(
this,"您确定要退出程序吗？","JNote"
,JOptionPane.YES_NO_OPTION); enable = (option==1);
} if(!enable){
//忽略其他事件，交给JFrame处理
super.processWindowEvent(e);
}
}

//事件处理
    private class NewHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String buttonName = e.getActionCommand(); 
            JOptionPane.showMessageDialog(null,buttonName + "被点击");
        }
    }
}