半田さんの以下の変更が原因のようですね。

2003-02-24 Kenichi Handa <handa@m17n.org>

* international/characters.el: Fix syntaxes of gb2312 and big5.

* language/japan-util.el (sentence-end-save): Variable deleted.
(setup-japanese-environment-internal): Don't setup sentence-end.
(exit-japanese-environment): Function deleted.

* language/japanese.el ("Japanese"): Delete `exit-function'.

* textmodes/paragraphs.el (sentence-end): Add Chinese and Japanese
characters.