On Aug 19, 2011, at 7:15 PM, Eli Zaretskii wrote:

>> From: Ivan Andrus <darthandrus@gmail.com>
>> Date: Fri, 19 Aug 2011 18:19:47 +0200
>> Cc: antoine.levitt@gmail.com,
>> 9324@debbugs.gnu.org
>> 
>> In case you are interested in what happens in my contaminated emacs, if I run C-x = after (forward-sexp) then it says a left parenthesis, but if I use `(progn (forward-sexp)(what-cursor-position))` then it says the next character is C-j.  Furthermore, changing it to (prog2 (forward-sexp) (what-cursor-position) (redisplay)) causes it to work properly (i.e. no bug).
> 
> If invoking `redisplay' fixes the problem, it means some display
> optimization is misfiring.  But there are quite a few of those
> optimizations, so without a reproducible test case, it's really hard
> to say where to look.
> 
>> I guess I'm probably on my own on this one, since even I can't reproduce it reliably in emacs -Q, so what functions that I should start debugging?
> 
> I agree with Antoine: if you can reliably reproduce this with your
> ~/..emacs, bisect it to find the minimal customizations necessary to
> reproduce the problem, then post that information here.

Okay, I think I can reliably reproduce it now.  Sorry it took so long to get it right.  Anyway it seems to require both highlight-parentheses-mode and hl-sexp-mode as well as a custom mode-line face.  I invoke it with:

emacs -Q -l ~/.emacs.d/elpa/highlight-parentheses-1.0.1/highlight-parentheses.el -l ~/.emacs.d/local/hl-sexp.el ~/vcs/emacs/bug-example-3.el

Thanks for your patience and pointers,
Ivan