Erroneous lighting remains in completely sealed room

when making a completely sealed room using a fill command, it was observed that a small patch of the room remained lit with what the F3 screen states as being "skylight".  

Steps to reproduce: 

1. launch version 1.18.2 creative world 
2. created large hollow box using the fill command one wall at the time 80*80*80 in size using black concrete 
3. bug occured on the inside bottom edge on the south wall

Patch does not update when:

exiting and reentering the world , restarting the game, attempting to update it using any lightsource, replacing blocks in the wall or ceiling of the cube in the affected area