Underground areas are lit by the sky when upgrading from 1.12.2

Make a world in 1.12.2

Upgrade to 18w21a

Most caves are lit by the sky now.

 

• Unable to determine what causes a cave to be lit*
• Updating area by placing/breaking won't fix it
• 1 Block change can sometimes fix an area, but undoing your block, area will be bugged again