FULL PRODUCT VERSION :
java version "1.7.0_40"
Java(TM) SE Runtime Environment (build 1.7.0_40-b43)
Java HotSpot(TM) 64-Bit Server VM (build 24.0-b56, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
OS X 10.8.5 (12F37)

A DESCRIPTION OF THE PROBLEM :
When a java application is using "apple.laf.useScreenMenuBar" to enable native menu, the accelerator keystroke combination Cmd-Enter (or Meta-Enter) will produce two ActionEvents

REGRESSION. Last worked in version 6u45


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.*;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JCheckBoxMenuItem;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.ButtonGroup;
import javax.swing.JMenuBar;
import javax.swing.KeyStroke;
import javax.swing.ImageIcon;

import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import javax.swing.JFrame;

public class MenuDemo implements ActionListener {
JTextArea output;
JScrollPane scrollPane;
String newline = "
";

public JMenuBar createMenuBar() {
JMenuBar menuBar;
JMenu menu;
JMenuItem menuItem;

menuBar = new JMenuBar();

menu = new JMenu("A Menu");
menu.setMnemonic(KeyEvent.VK_A);
menuBar.add(menu);

menuItem = new JMenuItem("Meta-Enter", KeyEvent.VK_E);
menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, ActionEvent.META_MASK));
menuItem.addActionListener(this);
menu.add(menuItem);

menuItem = new JMenuItem("Meta-E", KeyEvent.VK_E);
menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_E, ActionEvent.META_MASK));
menuItem.addActionListener(this);
menu.add(menuItem);

menuItem = new JMenuItem("ALT-Enter", KeyEvent.VK_E);
menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, ActionEvent.ALT_MASK));
menuItem.addActionListener(this);
menu.add(menuItem);return menuBar;
}

public Container createContentPane() {
JPanel contentPane = new JPanel(new BorderLayout());
contentPane.setOpaque(true);

output = new JTextArea(5, 30);
output.setEditable(false);
scrollPane = new JScrollPane(output);

contentPane.add(scrollPane, BorderLayout.CENTER);
return contentPane;
}

public void actionPerformed(ActionEvent e) {
JMenuItem source = (JMenuItem)(e.getSource());
String s = "Action event detected." + newline + " Event source: " + source.getText();
output.append(s + newline);
output.setCaretPosition(output.getDocument().getLength());
}

private static void createAndShowGUI() {
System.setProperty("apple.laf.useScreenMenuBar", "true");

JFrame frame = new JFrame("MenuDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

MenuDemo demo = new MenuDemo();
frame.setJMenuBar(demo.createMenuBar());
frame.setContentPane(demo.createContentPane());

frame.setSize(450, 260);
frame.setVisible(true);
}

public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
---------- END SOURCE ----------