A similiar failure can be observed when typing <some character>C-q 0  
3 2 3 <some non-decimal event> or <some character>C-q 1 4 4 3 in  
octal. In GNU Emacs 23.0.60 C-q 0 3 2 3 produces a COMBINING DOT  
BELOW, which is combined with the previously typed character. In the  
end something ugly appears, as shown above. In Emacs.app only a blank  
spot is left. C-u C-x = shows:

	        character: ̣ (803, #o1443, #x323)
	preferred charset: unicode (Unicode (ISO10646))
	       code point: 0x0323
	           syntax: w 	which means: word
	         category: ^:Combining
	Combining diacritic or mark
	      buffer code: #xCC #xA3
	        file code: #xCC #xA3 (encoded by coding system utf-8-unix)
	          display: composed to form "̣" (see below)
	
	Composed using this font:
	  nil:-apple-NimbusMonL-medium-normal-normal-Regular-10-*-*-*-*-*- 
iso10646-1
	by these glyphs:
	  [0 0 803 0 6 0 5 5 0 [0 0 6]]
	
	Character code properties: customize what to show
	  name: COMBINING DOT BELOW
	  old-name: NON-SPACING DOT BELOW
	  general-category: Mn (Mark, Nonspacing)
	
	There are text properties here:
	  fontified            t

Using a font like Lucida Grande that has ọ, o, and COMBINING DOT  
BELOW, I cannot compose ọ from o and COMBINING DOT BELOW. Again, in  
GNU Emacs 23.0.60 this at least creates something ugly.


In GNU Emacs 23.0.60.1 (powerpc-apple-darwin8.11.0, NS apple- 
appkit-824.48)
  of 2009-01-04 on localhost
Windowing system distributor `Apple', version 10.3.824
configured using `configure  '--without-sound' '--without-pop' '-- 
with-dbus' '--with-libotf' '--with-ns' '--disable-ns-self-contained'  
'--enable-locallisppath=/Library/Application Support/Emacs/ 
calendar23:/Library/Application Support/Emacs/caml:/Library/ 
Application Support/Emacs:/sw/share/emacs21/site-lisp/elib'  
'PKG_CONFIG_PATH=/sw/lib/xft2/lib/pkgconfig:/sw/lib/fontconfig2/lib/ 
pkgconfig:/sw/lib/freetype219/lib/pkgconfig:/sw/lib/pango-ft219/lib/ 
pkgconfig:/sw/lib/qt4-x11/lib/pkgconfig:/sw/lib/system-openssl/lib/ 
pkgconfig:/sw/lib/pkgconfig:/sw/share/pkgconfig:/usr/X11R6/lib/ 
pkgconfig:/usr/local/lib/pkgconfig:/usr/lib/pkgconfig' 'CFLAGS=-Wno- 
pointer-sign -bind_at_load -H -pipe -fPIC -mcpu=7450 -mtune=7450 - 
fast -mpim-altivec -ftree-vectorize -foptimize-register-move - 
freorder-blocks -freorder-blocks-and-partition -fthread-jumps - 
fpeephole -fno-crossjumping' 'CPPFLAGS=-no-cpp-precomp' 'LDFLAGS=- 
bind_at_load -dead_strip -multiply_defined suppress -L/sw/lib/ncurses''

Important settings:
   value of $LC_ALL: nil
   value of $LC_COLLATE: nil
   value of $LC_CTYPE: de_DE.UTF-8
   value of $LC_MESSAGES: nil
   value of $LC_MONETARY: nil
   value of $LC_NUMERIC: nil
   value of $LC_TIME: nil
   value of $LANG: de_DE.UTF-8
   value of $XMODIFIERS: nil
   locale-coding-system: utf-8-unix
   default-enable-multibyte-characters: t

Major mode: Grep

Minor modes in effect:
   show-paren-mode: t
   display-time-mode: t
   tooltip-mode: t
   tool-bar-mode: t
   mouse-wheel-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   global-auto-composition-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   column-number-mode: t
   line-number-mode: t
   transient-mark-mode: t

--
Greetings

   Pete

If we don't succeed, we run the risk of failure."
				– George W. Bush