You can make a test throw an anvil from a place high enough to kill the mob, when it falls it will not break
Comments 4
This is isnt a bug that is how anvils work. They only get damaged when they depending of the height of the fall but it doesn't break unless (maybe) if it lands on a non solid block (slabs, chests, fences, anything that isnt a full block) it can break and drop it.
Is this actually a bug? I've seen videos online where the anvil doesn't (or shouldn't) break once it touches the ground... unless there's a torch or slab underneath, it does not make sense for an anvil to break on a solid block.