http://bugs.winehq.org/show_bug.cgi?id=34056
--- Comment #1 from Sagawa sagawa.aki+winebugs@gmail.com 2013-07-14 12:10:56 CDT --- In my investigation, the application expects WM_CHAR or WM_IME_CHAR for inputting Japanese characters.
After the commit dc02e4, ImmSetOpenStatus isn't called under IBus XIM. Because IBus XIM server doesn't support PreEditStateNotify. Thus, UIWnd member isn't initialized. When the user finish selecting candidate, WM_IME_COMPOSITION is sent. However UIWnd is still NULL, it isn't relayed in DefIME_WindowProc. So, the application can't receive WM_IME_CHAR and WM_CHAR messages.
Before the commit dc02e4, it works well because every XIMPreEditStartCallback initialize UIWnd member by ImmSetOpenStatus.