Crashes servers using Bukkit patches ontop of forge (Ex Kettle: https://github.com/KettleFoundation/Kettle )
I've verified this crashes on Kettle and AtomMC.

Crash Log: https://pastebin.com/ruSLusbn

The problem seems to be caused of 2 reasons

1. Bukkit has patched methods that the CoreMod edits using ASM
2. Mappings seem to be different