AWT TextField Korean input seems broken in jdk7 (although fixed in Swing with 7045354).
I've observed described below on Windows XP sp3.

(1) Take an AWT test containing just a Frame with a TextArea, compile and run.
(2) Switch to Korean.
(3) Change Hangul mode in IME's language bar.
(4) Start typing "gks"
Now,
(4.1) in pre-b55 builds, say b51, you'll see a blinking ideogram in inverse colors just here at the caret position (see an attached image)
(4.2) in post b55 builds, say b140, the ideogram will be visible on the gray background at (0,0) -- again see another attached image.

In both cases (and with a special build provided for 7045354 as well) there will be no candidate window. If you press a number, 1 or 2, a correspondent candidate will be committed.