FULL PRODUCT VERSION :
java version "1.6.0-rc"

ADDITIONAL OS VERSION INFORMATION :
SunOS ahum2 5.10 Generic_Patch_118844-30 i86pc i386 i86pc


A DESCRIPTION OF THE PROBLEM :
I ran into this while devising a patch. If during the process of making a JPopupMenu visible an exeception is thrown interaction with the GNOME desktop appears to cease. I cannot click outside of the Java window, only inside of it. Im not sure if this is limited to GNOME/X but it certainly has an affect. Note, Ive target the setVisible method. It may well other methods in the call stack can cause this since Im uncertain as to the general cause beyond an exception at one point.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run this test on GNOME, see if your desktop become unresponsive.

PRESS THE EXIT BUTTON TO CLOSE THE WINDOW AND STOP THE UNREPSONSIVENESS

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
That the GNOME desktop won't be blocked.
ACTUAL -
its blocked

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "AWT-EventQueue-0" java.lang.AssertionError: What happened!!!
        at BoomJPopupMenu$1.setVisible(BoomJPopupMenu.java:12)
        at javax.swing.JPopupMenu.menuSelectionChanged(JPopupMenu.java:1438)
        at javax.swing.MenuSelectionManager.setSelectedPath(MenuSelectionManager.java:95)
        at javax.swing.MenuSelectionManager.clearSelectedPath(MenuSelectionManager.java:127)
        at javax.swing.plaf.basic.BasicPopupMenuUI$MouseGrabber.cancelPopupMenu(BasicPopupMenuUI.java:841)
        at javax.swing.plaf.basic.BasicPopupMenuUI$MouseGrabber.eventDispatched(BasicPopupMenuUI.java:773)
        at java.awt.Toolkit$SelectiveAWTEventListener.eventDispatched(Toolkit.java:2360)
        at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2252)
        at java.awt.Toolkit.notifyAWTEventListeners(Toolkit.java:2210)
        at java.awt.Component.dispatchEventImpl(Component.java:4308)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3983) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
        at java.awt.Container.dispatchEventImpl(Container.java:2102)
        at java.awt.Window.dispatchEventImpl(Window.java:2429)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160) at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class BoomJPopupMenu implements Runnable{

    public void run(){
JPanel jp = new JPanel();
        JPopupMenu jpm = new JPopupMenu(){
public void setVisible(boolean visible){
                    super.setVisible(visible);
                    throw new AssertionError("What happened!!!");
                }
};
        for(int i = 0; i < 10; i ++)
            jpm.add(new JMenuItem(String.valueOf(i)));
        jp.setComponentPopupMenu(jpm);
        JFrame jf = new JFrame();
        jf.add(jp);
        JButton jb = new JButton("Exit");
        jb.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
                    System.exit(0);
                }
});
        jf.add(jb, BorderLayout.SOUTH);
        jf.setSize(500,500);
        jf.setVisible(true);
    }

    public static void main(String ... args){
        SwingUtilities.invokeLater(new BoomJPopupMenu());
    }

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
maybe instrument setVisible to grab exceptions