This bug was already reported in:
This is NOT a duplicate of
MC-55730 (which seems to have been fixed in one of the 1.8 releases). We created a new issue since the other ones are all closed as duplicates of this one.
Steps to reproduce:
- Spawn a big (~50x50) stone platform using fill (you can build it by hand if you're brave enough)
- There are bright spots below the platform
The reason for this issue (and a fix) can be found here: https://github.com/MinecraftForge/MinecraftForge/pull/3870