Bright spots below /fill-ed platform

This bug was already reported in:

• MC-46129
• MC-81290
• MC-109120

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