Sky light levels underground too high (since 18w05a)

The bug

As you can see from the screenshots below, I am underground, fully enclosed with no sky access and the light level is like 8 all the way up to 14 in the first screenshot. For some reason lighting is bugged, and the lighting is going through all the blocks. I can also see thunder through the blocks. Because the light is going through the blocks, mobs can't spawn.