Run the testcase below,
you'll see the messageBox and the green trayicon appear

Click on the green trayIcon ->
ava.lang.ClassCastException: java.awt.TrayIcon cannot be cast to java.awt.Component
at javax.swing.plaf.basic.BasicPopupMenuUI$MouseGrabber.eventDispatched(BasicPopupMenuUI.java:810)
at java.awt.Toolkit$SelectiveAWTEventListener.eventDispatched(Toolkit.java:2376)
etc...

comes up

===Test case===

OS: Windows XP
JDK 6,7

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;

public class bug {
    public static void main(String[] args) throws Exception {
        SystemTray tray = SystemTray.getSystemTray();
        TrayIcon ti = new TrayIcon(getImage(), "Hello");
        tray.add(ti);
        
        final JPopupMenu popup = new JPopupMenu("Menu");
        popup.add(new JMenuItem("Item"));
        
        ti.addMouseListener(new MouseAdapter() {
            public void mouseReleased(MouseEvent e) {
                popup.setLocation(e.getX(), e.getY());
                popup.setVisible(true);
            }
        });
        
        JOptionPane.showMessageDialog(null, "message");
    }

    static Image getImage() {
        BufferedImage im = new BufferedImage(32, 35, BufferedImage.TYPE_INT_ARGB);
        Graphics2D g2 = (Graphics2D) im.getGraphics();
        g2.setColor(Color.GREEN);
        g2.fillRect(0, 0, im.getWidth(), im.getHeight());
        g2.dispose();
        return im;
    }
}