We've been shipping this patch for some time in Debian now. The problem
description from the patch header is reproduced below. You may want to note the
licensing issue mentioned below, but we've been shipping it because the method
by which this particular patch was generated and updated was also given below.

This patch by Denis Barbier.

WARNING: do not recode this file, it contains UTF-8 characters.

The X11 protocol states that Unicode keysyms are in the range
0x01000100 - 0x0110FFFF.  If the result of composing characters
is a Unicode codepoint, X returns the corresponding Unicode
keysym, which is its Unicode codepoint augmented by 0x01000000.
Latin-1 characters must not appear with their Unicode codepoints
in compose files, otherwise the returned composed character lies
in the range 0x01000000 - 0x010000FF which is not valid.

There are two solutions: either fix composing routines to return
0xZZ instead of 0x010000ZZ (where Z is an hexadecimal digit),
or replace U00ZZ by their corresponding keysyms in compose files.
The latter is more logical and less error prone, so compose
files will be patched.
Many applications accept these invalid Unicode keysyms, but few of
them don't, most notably xemacs.  Only UTF-8 locales are affected.

This has been fixed very recently in XFree86 CVS (but not xorg),
but for licensing reasons, this patch is not grabbed.
Instead automatic conversion is performed by:
  sed -e '/XK_LATIN1/,/XK_LATIN1/!d' /usr/X11R6/include/X11/keysymdef.h \
  | grep -v deprecated | grep 0x0 \
  | sed -e 's/0x0/U0/' -e 's/XK_//' \
  | awk '{ printf "s/\\b%s\\b/%s/ig\n", $3, $2; }' > sedfile
  for f in *.UTF-8
  do
    sed -f sedfile $f > $f.tmp && mv $f.tmp $f
  done