I have found a bug.
Usually, if Landfill is recoverable by mining it, you get the Landfill back when you mine it.
But, if you place Landfill, then place anything on top of the Landfill (like a furnace or chest, pretty much what I only tested it with) then remove the thing ontop of the Landfill, removing the Landfill doesn't recover it. You lose the Landfill permanently.
Not sure if that is intentional behaviour.
