Cannot compose commit message in Japanese with IME.

Strange UI feedback:

• Types all ascii-latin1 characters are OK.
• Try ascii-latin1 and compose with Japanese-IME, cannot enable IME.
• Copy Japanese character from another text editor, then paste this character in commit window, it works right after that, IME too.

• This problem come from version 1.6.1, 1.4.* are no problem.