The bug

In a previous version the lighting engine was moved to a separate thread. However it appears there is nothing which prevents desync between the gameplay and the lighting thread.

This can cause all kind of unexpected behavior, for example:

• Being unable to plant crops in lit up caves
• Monters spawning in lit up areas
• Stopping the server / closing a world when the lighting thread has not caught up causes pending light updates to get lost

How to reproduce

1. Place a repeating command block (always active), pointing upwards

   fill ~ 255 ~ ~20 255 ~20 stone
   

2. Place a chain command block above (always active)

   fill ~ 255 ~ ~20 255 ~20 air
   

3. Set the time to night

   /time set night
   

4. Open the debug screen (F3)
5. Place a light source, e.g. a torch
   The "block" value for "Server light" does not change
6. Reopen the world
   The area around the light source is not lit up