I had a wooden slab and I put it on another slab whicg made the slab block. So, I broke it and instead of giving me two slabs, it gave me two Wood Planks and it said some kind of code. You can see the name of the block in the image. Also, anytime I place it down and mine it again, it gets me two. It doesn't affect gameplay but it's just a bug that's a little weird.