The problem is observed on Windows 00/NT/XP (ZH).

To reproduce:

1. Open an active component (other types of components probably ok to use too).
2. Select some JAVA IM, like CityIM or Wubi, type in some characteres.
3. Switch to HOST IM, type in some caharters. (this time the switching should work fine).
4. Repeat steps 1 and 2. This time HOST IM fails to switch.

Sometimes it helps to press additional 'CTRL SPACE' or some other switching key combination, depending on the IM; however, the behavior is rather random.