Strange interaction of glow and floor in DE-Raytracer

[Feline]

There's something going on with glow and floors in DE-Raytracer that is probably best just demonstrated.

Open the attached fragment - it's a distance estimator and coloring that simply look like this:


vec3 baseColor(vec3 p, vec3 q) {
    return p;
}
float DE(vec3 pos) {
       return length(pos)-1;
}

- Note the green stuff in the upper middle of the screen
- Go to the "Floor" tab and toggle the floor on/off
- Go to the "Light" tab (with the floor on) and slowly increase "GlowMax" to 1, 2, 5, 10 ...
- Finally, with floor "on" and GlowMax <10 hit "Dither = 1"

I'm not clear what, exactly, is going on here, I figured someone out there might have an insight...