[BUG] Floor+ceiling rendering glitches in area using transfer heights in KDiZD

[Macil]

GZDoom version

Gzdoom 4.12.2

Which game are you running with GZDoom?

Doom

What Operating System are you using?

Windows 11

Please describe your specific OS version

Windows 11

Relevant hardware info

AMD cpu, Nvidia 2080 Ti

Have you checked that no other similar issue already exists?

• I have searched and not found similar issues.

A clear and concise description of what the bug is.

There's a specific area in Knee-Deep in ZDoom (2012 release) map Z1M6 that renders incorrectly depending on where you're standing and the angle you're looking.

The affected sectors all have deep slime, done by using the Transfer Heights line special. Not all of the deep slime sectors are equally affected. There don't seem to be any differences between the affected slime sectors and the unaffected slime sectors (almost all of them have the same sector tag, 47, and are affected by the same line special).

There's also a second parallel area on the map the same exact rendering bug happens, about 50 feet west. (I was not able to reproduce the rendering bug on the two similar skylight-over-slime areas on the north side.)

I've tested using the Vulkan, OpenGL, OpenGL ES, and software renderers. The bug is present in all but software rendering.

What it's supposed to look like:

Near my reticle in the above image is a gray ledge going around the slime. The rendering bug is visible if you run along that ledge and look at the slime below the skylight or look up at the skylight:

While standing in that exact position, if I look around a little then glitched sectors close to the bridge sometimes fix themselves:

Ceiling view: (notice the skylight ceiling is glitched, but also part of the archway to the right is glitched too; specifically the part of it that's above the slime)

How the ceiling should look:

Automap view:

Steps to reproduce the behaviour.

Run Knee-Deep in ZDoom (2012 release) with Doom 1 and load save04.zip (or go to map z1m6 and go forward through the map to find the location pictured above, you can't miss it)

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