Its not the chunk, its only 1 block in the spawnroom which doesnt update its lightvalues untill you force it to do so. The easiest way to locate the block is to make it dark and try to see the center of the light, then go and place a block in this center, break it and boom - darkness.
I went around checking blocks there are multiple broken light level areas and they break both ways.
Place block BAM update break it and flip the switch and it breaks again. I spent a good two hours working on possible ways to fix this. I even filled the whole room up and re dig it out and still the lighting bug stays.