> From: Eric Hanchrow <eric.hanchrow@gmail.com>
> Date: Sun, 13 Dec 2015 17:54:04 +0000
> Cc: 22120@debbugs.gnu.org
>
>     Looks like another reincarnation of bug#21667.
>
> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21667 appears to be unrelated to
> this one. I suspect you made a typo.

Sorry, I meant 21666.

>     Can you modify lui-adjust-undo-list so that GC is inhibited (by
>     binding gc-cons-threshold to most-positive-fixnum around the whole
>     function)?
>
> OK, I've done that. If that works, it'll take days of use before I'm confident
> that it did work (because the bug only appears once every few days); can you
> think of some sort of debug message I can stick in there that can tell us that
> you've correctly guessed the cause?

No, I don't think it's possible, not during GC anyway.

There's no hurry, so waiting for this to happen is fine.  Thanks.