Sorry that I can't be more clear about what happened: after putting a lamp directly below another lamp (both pointed downward), and having both turned on, then I broke the first lamp and later the second lamp. Afterward, there was a remaining invisible light block.

What made it strange was that it wasn't just like a normal, "forgotten" block - which normally, I could place some other block in its place, then destroy that and have the light be gone. In this case, I could place a block in the invisible block's position and the light would indeed go away, but it would come back after breaking the opaque block. It's as if your mod thought that one invisible light was still in need of regenerating.

If needed, later, I could test more.

Ah I think I see what happened there. Will release a fix for that soonish. For fixing this you might to need to place the lamps again after updating then turn them on and off once. In a later version I will implement a command to reset all lights.

Yes, putting a lamp back in the 1st position and turning it on/off made the block go away for good.

The next release will include a fix for that not happening again.