Yep. I was raising this more as a bug. I’ve been assuming that if an item causes the receiving window in a processor (like a grinder or a campfire) to light up green (as opposed to red), that means it has some sort of role to play using that processor. If the window stays red, that means you can’t use the item. I hope that’s right.
If it is, it seems the grinder, crusher and extraction furnace are not correctly responding to Common Reedmace.