chunk light problem

When building the countryside, I found a loophole in brightness. At the end of the block (16x256x16), I built the brightness of the torch and so on at 13 locations in the block, but the blocks after 16 did not embellish brightness.
What I hope to happen is...
After the torch is placed, there is brightness outside the block.

What actually happened is...
The torch is at the boundary of the block (not the world boundary), away from 4 places to build the torch. You will find that the brightness is stopped and dark.

Steps to Reproduce:
1. find a dark area
2. the block boundary (F3 + N) in the dark area
3.A square with a luminance (for example; a sea crystal lamp).

4.You will find that the brightness of the outside is not updated ,only the brightness inside is updated

The following screenshot can prove the Bug

Yes, this is my first report. Fix this loophole, thank you Mojang. (sorry I didn't learn English, I'm Chinese).🙂