Preface: I briefly skimmed through to check for duplicates, but I did not find any. I apologize if this has already been reported.

Issue #1: Server with custom map using Spigot (issue also occurred without plugins [no screenshots])

A mob farm I made had an interesting issue; even when completely sealed, the room appeared fully lit by the sun with light levels of 15 and 14. Slabs on the roof were replaced, block material was replaced, lighting updates with torches and water was attempted, but nothing could make the room dark. Interestingly, a room built on top of this was dark. Connecting the two rooms however continued the light up above into the dark ceiling of the initial taller room. Unfortunately I have no pictures, so hopefully this description will do.

Issue #2: Single player redstone ready flat land

A room with redstone lamps + stained glass has a very interesting lighting glitch that can only be temporarily resolved by relogging into the world. Once the redstone lamps are activated and deactivated, two neighboring chunks do not update simultaneously. One chunk updates to dark, while the bordering remains completely lit as if the lamps were still active. Note that all lamps are in fact disabled when this occurs, the lighting should not be present yet the game treats it as though it is. The screenshots depict this issue with more depth.