When smelting sponge with more than 1 bucket in "fuel" space, buckets will disappear

If you put more than one bucket in the fuel slot of a furnace after activating it with a different fuel source, when the bucket gets filled with water, you will lose all of the other buckets. A possible fix to this is to only let the player put one bucket in the furnace at once, as this is caused because water buckets do not stack.