Mouse over composite character of display text property

[Fujii Hironori]

My Emacs21 always crashes if mouse cursor moves over a composite character
of a display text property.

(defun MY-put-composite-char-display-text-property-region (start end)
  (interactive "r")
  (put-text-property start end
                     'display (compose-string "a'")))

In GNU Emacs 21.3.2 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-04-25 on raven, modified by Debian
configured using `configure  i386-linux --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes --with-x=yes
 --with-x-toolkit=athena --without-gif'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: en_US
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: en_US
  value of $LANG: ja_JP
  locale-coding-system: japanese-iso-8bit
  default-enable-multibyte-characters: t