Tried in a fresh 1.21 All the mods 5 single player world in creative by placing down the swamp homi and mossy cobblestone, mossy stone bricks and quarks cobblestone bricks and the moss is not being stripped off them.

Forge 31.1.63
Minecraft 1.15.2
All the mods 5 1.21 modpack on curse

Not sure if there has been a mechanic update or if it is broken
I did check the book and there wasn't a mention of anything new in the description so I am assuming it's a bug.

Thank you for your time