Furnace mistakes woods!
If you use a furnace and add to the first/second slot a oak wood, and then in the same slot you add a spruce or birch wood (without taking out the oak wood), it will convert the spruce/birch into oak wood!
If you use a furnace and add to the first/second slot a oak wood, and then in the same slot you add a spruce or birch wood (without taking out the oak wood), it will convert the spruce/birch into oak wood!