BuildCraft|Core

Might be a method with a broken method name vs obfuscated name.

what forge version you using? i know there where some issues and fixes of this in the past with forge

if you have a recent version i putting the method names on the forge forums, someone will recognize it if it's a clash

I was using Forge 13.20.0.2226 when I discovered this.

From some more testing it looks like this was caused by comparing itemstacks to null in

Line 90 in afe5114

    
           if (playerStack != null && (slot.getStack() == null || ((IPhantomSlot) slot).canAdjust())) {

. I have no idea how it worked in a dev before, so we might come across another related problem later.

(Fixed in 68fef6e)