Textures shiver after scrolleg long enough

[simc]

GZDoom 4.7.0pre-136 - 4.3.1.
Softpoly, Opengl and Vulkan.
Doom software and True color SW mode but not Hardware accelerated mode.

If a wall texture is scrolled vertically long enough the texture starts to shiver and twitch unusually when the player moves and approaches it.

This starts to happen after scrolling some 8000 map units and it's strength increases as the scrolling distance grows. If the scrolling is slow enough the effect can be seen during the scrolling too. Horizontal scrolling and the scrolling speed doesn't seem to have an effect on this.

The test wad below has two setups. On the left is a Boom displacement scroller which moves the wall 20k mu (takes 10 seconds). On the right is an accelerative scroller (65k mu, 5 seconds). Start GZDoom without config and hit the switches. From the console: vid_rendermode 0 or 1. Or from the Options > Set Video Mode select Render Mode: Doom Software Renderer or True Color SW.