Dead keys still not working in GTK Emacs

[Ian D. Leroux <idleroux%fastmail.fm@localhost>]

For years now I have been trying to track down a bug in dead key
handling in emacs-gtk with UTF-8 locales.  For the historically
minded, the original netbsd-users thread starts at
http://mail-index.netbsd.org/netbsd-users/2010/11/03/msg007046.html
while the subsequent discussion with the upstream maintainers is here:
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=7380
Progress has been slow because upstream cannot reproduce the bug, and
I have no experience of X11 programming.

To recap, the problem I see is that dead keys, such as ` on the
us-international keyboard, give me error messages like <dead-grave is
undefined> instead of being combined with the following character.
Poking around with gdb has so far revealed that XIM is somehow
disabled on the emacs window, which consequently tries to use the
latin1-only XLookupString API instead of the unicode-enabled
XmbLookupString.

The problem is specific to emacs: firefox, urxvt, and xterm handle
dead keys correctly.  I am running NetBSD/amd64 -current, with current
pkgsrc.  Possibly relevant environment variables:
LC_CTYPE=en_US.UTF-8
LC_COLLATE=C
LC_NUMERIC=C

I'm out of my depth, and would appreciate some help.
1- Can anyone else reproduce this bug?  I'd like to find out if it is
  NetBSD specific, amd64-specific, configuration-specific ...
  If dead keys in emacs-gtk work for you and you use a UTF-8 locale, I
  would still like to hear from you.  The more known-good
  configurations I know about, the better I can constrain the problem.
2- Are there any configuration files that should be present for XIM or
  other bits of xkb to work?
3- If anyone has some X11 programming expertise and a little time to
  spare, I could use some guidance.

Thanks,

-- IDL