bug#41187: 28.0.50; Flipped text

[Alan Third]

On Mon, May 11, 2020 at 01:00:57PM +0100, Wasim Abbas wrote:
> 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.

I'm short on ideas with this, but can you tell whether the text that
displays upside down is text that was already on screen (and therefore
has probably been copied), or is newly drawn?
-- 
Alan Third