Meanwhile, here is Copypasta of my reply to Romullus on mantis, in case anyone could use these temporary workarounds:
Hi, I've successfully reproduced it and Ondra found out what the problem is. Basically all textures on lights outside of the camera frustrum get sampled at a lower resolution, resulting loss of precision.
Ondra said it will be fixable, but it will take a while.
There are several workarounds, like using CoronaLightMTL instead of CoronaLight and putting rayswitch map inside, where map in GI slot would be blurred (averaged) version of your orange dots map.
This map is also the reason why this bug is so extreme in this scene. Sampling those small orange dots instead of hitting black at downsized resolution is quite hard.
BUT, what i found out to be most efficient workaround is actually using CoronaBitmap. It has better filtering than Max's native bitmap, so just right click your "dot light" gradient map in slate editor, and select render map. That will collapse the procedural map into bitmap. Select resolution, i used 500*500.
Then load this rendered map into CoronaBitmap, and put this CoronaBitmap as texture for that CoronaLight. I've just tried it and it seems to work well :)
