1. enter the nether
2. travel off to a distance

after some time you will see that lava and glowstone don't emmit light. they will start to emmiting back again after a while (no player interaction with the chunk). that means the lighing loads slower than the terrain

you should see the lighing to be there properly.

edit: thry to place your own lighing source down. you will see that the lighing effect doesn't load imediatly, but it loads from chiunk to chunk. ( very noticebale when removing the light source.

The video issues the problem using a fire.