FULL PRODUCT VERSION :
java version "1.6.0_15"
Java(TM) SE Runtime Environment (build 1.6.0_15-b03)
Java HotSpot(TM) Client VM (build 14.1-b02, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
Mnemonic disappears after repeated attempts to open menu items using mnemonic key:

Problem:
When you press a sequence of hot keys/ mnemonics, Panels stop displaying the Mnemonics for the menu items.

Sample scenario, press Alt+F, Alt+S (No action in between like mouse click or esc) the Mnemonics letters doesn't get displayed. (chose 'F' & 'S' as sample code below use same mnemonics.

Problem is reproducible only with "SystemLAF", but if we use "Metal/Motif LAF" then we do not have this problem as the menus appear differently.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Sample scenario, press Alt+F, Alt+S (No action in between like mouse click or esc) the Mnemonics letters doesn't get displayed. (chose 'F' & 'S' as sample code below use same )won't get displayed, after the very first time for which mnemonics get displayed.




EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected Results:
No matter how many ever times the mnemonics/hot keys are tried to access by pressing Alt+F or Alt+(any mnemonic present in menu item),particular mnemonic should get displayed/underlined properly.

ACTUAL -
Actual Result:
Alt+(any mnemonic present in menu item). it should get displayed/underlined every time the operation is performed.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
No error messages logged.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;



class MenuActionListener implements ActionListener {
  public void actionPerformed(ActionEvent actionEvent) {
    System.out.println("Selected: " + actionEvent.getActionCommand());
  }
}

public class MenuLookDemo {

  public static void main(final String args[]) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException {
    ActionListener menuListener = new MenuActionListener();
    JFrame frame = new JFrame("Menu Look Demo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
    JMenuBar menuBar = new JMenuBar();
    
    // used to set to Windows LAF
    String systemLAF;
    systemLAF = UIManager.getSystemLookAndFeelClassName();
    UIManager.setLookAndFeel(systemLAF);
    

    // First Menu, F - Mnemonic
    JMenu firstMenu = new JMenu("Fisrt Menu");
    firstMenu.setMnemonic(KeyEvent.VK_F);
    menuBar.add(firstMenu);
   

    // Fisrt Menu - menu items
    JMenuItem oneMenuItem = new JMenuItem("One", KeyEvent.VK_O);
    oneMenuItem.addActionListener(menuListener);
    firstMenu.add(oneMenuItem);

    JMenuItem twoMenuItem = new JMenuItem("Two", KeyEvent.VK_T);
    twoMenuItem.addActionListener(menuListener);
    firstMenu.add(twoMenuItem);
    
    // Second Menu, S - Mnemonic
    JMenu secondMenu = new JMenu("Second Menu");
    secondMenu.setMnemonic(KeyEvent.VK_S);
    menuBar.add(secondMenu);
    
    // Second Menu - menu items
    JMenuItem anotherMenuItem = new JMenuItem("Another Menu Item", KeyEvent.VK_A);
    anotherMenuItem.addActionListener(menuListener);
    secondMenu.add(anotherMenuItem);

    frame.setJMenuBar(menuBar);
    frame.setSize(350, 250);
    frame.setVisible(true);
  }
}


---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Workaround:
Disabling Windows Keyboard Navigation checkbox on display setting, will always shows mnemonics. I just tried to disable this option (control panel->display->Appearance->effects-> Hide underlined letters for keyboard Navigation until i press the Alt Key) and mnemonics always appears and able to use it properly.

SUPPORT :
YES