bug#23871: 25.1.50; Undo unexpectedly leads to blank buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Markus Triska <triska@metalevel.at>
> Date: Wed, 29 Jun 2016 23:47:19 +0200
> 
> In summary, step 8 leads to 2 problems:
> 
> (a) a blank buffer is shown
> (b) point position after the undo is not where point was before the insertion.

I suspect this is a redisplay problem, not an undo problem.  How do
you see that point is in the wrong position?  What does "C-x =" say
immediately after the undo?

Anyway, I tried to reproduce the problem, but couldn't: SWI-Prolog
7.3.x seems not to support the OS of my main development machine, and
all my attempts to simulate the situation by having a subprocess
insert a long string into a buffer failed: after undo I always see a
window with the single original line, the one that corresponds to your
line 15.  As expected.

Can you try coming up with a recipe that doesn't involve SWI-Prolog?

Also, how important is it to have exactly the font you mention and
exactly that size?  (I tried that font and that size, as well as a few
others, but that didn't help in my case.)

Thanks.