Lighting is incorrectly calculated with leaves above a certain height. Sky light under a leaf structure is brighter than it should be. When quitting the game and entering the map again, the lighting is correctly set, but when going under the structure, in the same chunks, the glitch happens again.
To reproduce the bug, create a flat world and build a square leaf structure at least 32 blocks above the ground. Quit and enter the map. Then go under the structure and fly up to the structure. This will trigger the glitch. I did it with the ground at Y=4 and the leaves at Y=32.