ADDITIONAL SYSTEM INFORMATION :
Also replicates in pre-release Java 22.

A DESCRIPTION OF THE PROBLEM :
The right-option key on a Mac keyboard does not behave consistent with the left-option key and other paired modifier keys. It fails to generate a keyReleased event (instead it seems to generate a second keyPressed event when the key is released). Also, getKeyLocation() reports as KeyEvent.KEY_LOCATION_STANDARD rather than KeyEvent.KEY_LOCATION_RIGHT.

This is observed in recent versions of Java. Running the same test under Java 14 produces a different result. The keyReleased event and key location are reported correctly. However, the keycodes for the right-Option key are completely different from the left-Option key, which is not the same for other modifier keys.

REGRESSION : Last worked in version 14

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the test case program (see source below) on a MacOS machine. Press and Release the right-option key and other modifier keys, left and right.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Key Pressed and Released events should be generated as appropriate. Key location should be "left" and "right" depending on which modifier key is pressed.

ACTUAL -
Pressing & releasing left-option and other modifier keys, such as left or right-shift, reports "Pressed" & "Released". Pressing right-option reports "Pressed" but releasing it does not report "Released", status remains as Pressed.

 Also notice that the Location of the right-option key is reported as "Standard" but all other paired modifier keys report as "left" or "right".

---------- BEGIN SOURCE ----------
package events;

/*
 * KeyEventDemo
 */

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;

class KeyEventDemo extends JFrame
        implements KeyListener,
        ActionListener
{
    JTextArea displayArea;
    JTextField typingArea;
    static final String newline = System.getProperty("line.separator");

    public static void main(String[] args) {
        /* Use an appropriate Look and Feel */
        try {
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
            UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        } catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        } catch (IllegalAccessException ex) {
            ex.printStackTrace();
        } catch (InstantiationException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        /* Turn off metal's use of bold fonts */
        UIManager.put("swing.boldMetal", Boolean.FALSE);

        //Schedule a job for event dispatch thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    /**
     * Create the GUI and show it. For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        KeyEventDemo frame = new KeyEventDemo("KeyEventDemo (Java " + System.getProperty("java.version") + ")");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Set up the content pane.
        frame.addComponentsToPane();


        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    private void addComponentsToPane() {

        JButton button = new JButton("Clear");
        button.addActionListener(this);

        typingArea = new JTextField(20);
        typingArea.addKeyListener(this);

        //Uncomment this if you wish to turn off focus
        //traversal. The focus subsystem consumes
        //focus traversal keys, such as Tab and Shift Tab.
        //If you uncomment the following line of code, this
        //disables focus traversal and the Tab events will
        //become available to the key event listener.
        //typingArea.setFocusTraversalKeysEnabled(false);

        displayArea = new JTextArea();
        displayArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(displayArea);
        scrollPane.setPreferredSize(new Dimension(375, 125));

        getContentPane().add(typingArea, BorderLayout.PAGE_START);
        getContentPane().add(scrollPane, BorderLayout.CENTER);
        getContentPane().add(button, BorderLayout.PAGE_END);
    }

    public KeyEventDemo(String name) {
        super(name);
    }


    /** Handle the key typed event from the text field. */
    public void keyTyped(KeyEvent e) {
        displayInfo(e, "KEY TYPED: ");
    }

    /** Handle the key pressed event from the text field. */
    public void keyPressed(KeyEvent e) {
        displayInfo(e, "KEY PRESSED: ");
    }

    /** Handle the key released event from the text field. */
    public void keyReleased(KeyEvent e) {
        displayInfo(e, "KEY RELEASED: ");
    }

    /** Handle the button click. */
    public void actionPerformed(ActionEvent e) {
        //Clear the text components.
        displayArea.setText("");
        typingArea.setText("");

        //Return the focus to the typing area.
        typingArea.requestFocusInWindow();
    }

    /*
     * We have to jump through some hoops to avoid
     * trying to print non-printing characters
     * such as Shift. (Not only do they not print,
     * but if you put them in a String, the characters
     * afterward won't show up in the text area.)
     */
    private void displayInfo(KeyEvent e, String keyStatus){

        //You should only rely on the key char if the event
        //is a key typed event.
        int id = e.getID();
        String keyString;
        if (id == KeyEvent.KEY_TYPED) {
            char c = e.getKeyChar();
            keyString = "key character = '" + c + "'";
        } else {
            int keyCode = e.getKeyCode();
            keyString = "key code = " + keyCode
                    + " ("
                    + KeyEvent.getKeyText(keyCode)
                    + ")";
        }

        int modifiersEx = e.getModifiersEx();
        String modString = "extended modifiers = " + modifiersEx;
        String tmpString = KeyEvent.getModifiersExText(modifiersEx);
        if (tmpString.length() > 0) {
            modString += " (" + tmpString + ")";
        } else {
            modString += " (no extended modifiers)";
        }

        String actionString = "action key? ";
        if (e.isActionKey()) {
            actionString += "YES";
        } else {
            actionString += "NO";
        }

        String locationString = "key location: ";
        int location = e.getKeyLocation();
        if (location == KeyEvent.KEY_LOCATION_STANDARD) {
            locationString += "standard";
        } else if (location == KeyEvent.KEY_LOCATION_LEFT) {
            locationString += "left";
        } else if (location == KeyEvent.KEY_LOCATION_RIGHT) {
            locationString += "right";
        } else if (location == KeyEvent.KEY_LOCATION_NUMPAD) {
            locationString += "numpad";
        } else { // (location == KeyEvent.KEY_LOCATION_UNKNOWN)
            locationString += "unknown";
        }

        displayArea.append(keyStatus + newline
                + " " + keyString + newline
                + " " + modString + newline
                + " " + actionString + newline
                + " " + locationString + newline);
        displayArea.setCaretPosition(displayArea.getDocument().getLength());
    }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Not known.

FREQUENCY : always