On Sun, Oct 27, 2019 at 11:49:20AM +0000, HaiJun Zhang wrote:
> After some debugging work, I think I find the cause.
> 
> See the discussion: https://lists.gnu.org/archive/html/emacs-devel/2019-10/msg01096.html

Thanks for working this out. I suspect that we can remove a call to
delete the working text from the C code and just leave it to lisp.

Please try the attached patch.
-- 
Alan Third