ZDoom

Much obliged,
worked like a charm!

As a workaround set custom inverse map to true under display options or play with LZDoom.
The link you posted is unrelated to this bug.

I'm having the same problem with v4.5.0, but am a complete illiterate tech moron and have no idea what any of the above means.
Can someone break this all down for a poor newbtard just tryin to play some Doom???

PS
Have also tried this older fix below but my console does not seem to recognize the applicable CVARs
https://www.doomworld.com/forum/topic/63209-invul-sphere-glitch-solved/

I'm running Win10 64-bit if that matters....

Keeping the clamp only for MainFP also works as expected, it's not possible to reverse the colormap with the clamp.

"It's fixed reverting this commit" (tm): :P
https://github.com/coelckers/gzdoom/commit/43562c94d0846153dadcf82859a6140653e713b7

But now why was the clamp required? @dpJudas

Version 4.5.0, i get a white screen with invulnerability on every render mode.
No, wait it's in 4.4.2 too! And in 4.3.3!
Edit: at least custom inverse colormap works. In 4.3.2 it doesn't happen but it's like the lightamp and the custom colormap doesn't work.