Charset lib and storage versions: 0.3.4
Forge version: 1.10.2-12.18.3.2185

Notes from testing:
I disabled Forestry, Botania, and Natural Pledge in my pack; the barrels got registered.
I enabled Forestry, and the barrels were still being registered.
I disabled Forestry and enabled Botania, and the barrels vanished

List of JARs present: imgur/tvkWfB2

I could not reproduce the issue with just Botania and Charset in my testing environment.

The code related to this has been rewritten probably almost entirely by now. For the time being, I'm closing it.