OPERATING SYSTEM(S):
--------------------
Japanese Windows 2000 Professional

FULL JDK VERSION(S):
-------------------
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:
------------
IME Composition window is disappeared during focus change operation on Japanese Windows 2000.

Steps to Recreate:

1. Compile and run attached testcase on Japanese Windows 2000
   > javac JCompTest.java
   > java JCompTest aaa bbb
2. Move input focus to "aaa" window and turn on IME
3. Move input focus to "bbb" window and turn on IME
4. Move input focus to "aaa" window and type "a",
   then Japanese "A" is displayed left-bottom on "aaa" window,
   then press Space key twice to dispplay candidate window
5. Move input focus to "bbb" window and type "i",
   then Japanese "i" is displayed left-bottom on "bbb" window,
   then press Space key twice to dispplay candidate window
6. Move input focus to "aaa" window, composition window and
   candidate window should be displayed, but only candidate window
   it displayed. <== PROBLEM

=====================================================================
import java.awt.*;
import javax.swing.*;

class JCompTest extends JFrame {
  JCompTest(String title, int x, int y, int width, int height) {
    setTitle(title);
    getContentPane().add(new JButton("JButton"));
    setSize(width, height);
    setLocation(x, y);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
  }
  static public void main(String[] args) {
    int x = 0, y = 0, offset = 200, w = 200, h = 100;
    for(String title : args) {
      new JCompTest(title, x, y, w, h);
      x+=offset;
    }
  }
}
=====================================================================

I could not recreate this problem on Japanese Windows XP