webstart swing components are occasionally repainted to wrong window.

OS: Windows XP SP3
Java: JRE6u16

swing components like JButtont, JScrollBar occasionally won't be repainted by mouse/key event.
And the component image is sometimes painted to wrong position that is not on component's window.

This issue was originally reported by the customer who run their own webstart application.
But the issue was able to be replicated on my lab system with our sample webstart application.

JWSFileChooserDemo:
  http://download.oracle.com/javase/tutorialJWS/uiswing/components/ex6/JWSFileChooserDemo.jnlp

Please find URL of the screenshot at comment section of this CR.

How To Reproduce:
  1) Launch JWSFileChooserDemo demo app using brower or javaws command.
  2) Click on Open a File Button.
     Security Alert dialog window will appear.
  3) Click another window so that focus moves to the another window.
     (e.g. command prompt, explorer..)
  4) Press OK button for security alert dialog window.
     File Chooser windows will appear.
  5) Click another window.
  6) Select one of file on chooser window and click open button.

Then, repeart Step 2) - 6).
Frequency of reproduction is very rare. It might need thousands of trials.

Even the issue happen, the situation can be restored if you iconify and deiconify the window.
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