This is reproducible with the latest mustang build. Not reproducible in Tiger. Occurs only on Windows platform.

The attached testcase opens up several top level windows - Frames, Dialogs and Windows and disposes all of them. This is done repeatedly over a period of time. After about 1-2 hours, the testcase throws the following exception:

java.lang.reflect.InvocationTargetException
         at java.awt.EventQueue.invokeAndWait(EventQueue.java:992)
         at TopLevelsNewTest.showDialog(TopLevelsNewTest.java:99)
         at TopLevelsNewTest.doTopLevelsTest(TopLevelsNewTest.java:63)
         at TopLevelsNewTest.doTest(TopLevelsNewTest.java:50)
         at TopLevelsNewTest.main(TopLevelsNewTest.java:24)
 Caused by: java.lang.InternalError: Invalid window handle.
         at sun.awt.windows.WToolkit.eventLoop(Native Method)
         at sun.awt.windows.WToolkit.run(WToolkit.java:290)
         at java.lang.Thread.run(Thread.java:620)