On Browser Plugin, sometimes Java cannot receive input focus

OPERATING SYSTEM(S):
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Red Hat Enterprise Linux 5 (Japanese Environment)

FULL JDK VERSION(S):
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java version "1.6.0_03"
Java(TM) SE Runtime Environment (build 1.6.0_03-b05)
Java HotSpot(TM) Client VM (build 1.6.0_03-b05, mixed mode)

DESCRIPTION:
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On Browser Plugin, sometimes Java cannot receive input focus after JDialog is displayed.

Steps to Recreate:

(Please run following commands on Japanese environment)

1. Create Java Plugin soft link
   $ ln -sf $JRE_HOME/plugin/i386/ns7/libjavaplugin_oji.so $HOME/.mozilla/plugins/
2. Change directory to demo/jfc/SwingSet2 directory
   $ cd $JRE_HOME/../demo/jfc/SwingSet2
3. Start Browser Plugin
   $ firefox $PWD/SwingSet2.html
4. On Icon List, press JOptionPane Demo button (7th button from Left-side)
5. Click "Show Input Dialog" button by mouse
6. Press Enter key to press "OK" button
7. Press Space key to press "Show Input Dialog"
8. Try 6 - 7, several times, then you cannot press button by Enter or
   Space key <== PROBLEM