bug#41187: 28.0.50; Flipped text

[Eli Zaretskii]

> From: Wasim Abbas <abbas.wasim@gmail.com>
> Date: Mon, 11 May 2020 13:00:57 +0100
> 
> I am seeing this issue on emacs head. The text randomly flips vertically. 
> Very hard to reproduce. But if you open a very long C/C++ file like 
> https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h
>  
> <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h>
>  and keep moving around the buffer, cut 100ish lines and paste in another 
> location and then move around again. You might hit the issue.
> 
> Here is a screenshot of it. I haven’t tried with emacs -Q yet but happy to 
> try if required. 

Wow!  That's got to be some weird problem with you video driver or the
display hardware.  Emacs never does anything like that.