I have not met exactly the blocks you are talking about, but I have met others that are similar. In the inventory they look like an oak slab on a red background, but on the hotbar they look like red squares. They also have the name "stone slab". But in the game it looks like an ordinary wooden slab, but no matter how I put it, it is always shifted half a block up. When I combined them, they didn't turn into a whole block. It is noteworthy that I got them without using cheats. I don't remember exactly how I got them, but I played on version 0.6.0.
These blocks became canonized as smooth stone blocks in 1.14. They're a decent building block but expensive to obtain as you need to smelt cobblestone twice, or use silk touch on stone and then smelt once. I mostly relegate smooth stone to its crafting uses like armour stands and blast furnaces, and use smooth andesite or diorite instead.
I have not met exactly the blocks you are talking about, but I have met others that are similar. In the inventory they look like an oak slab on a red background, but on the hotbar they look like red squares. They also have the name "stone slab". But in the game it looks like an ordinary wooden slab, but no matter how I put it, it is always shifted half a block up. When I combined them, they didn't turn into a whole block. It is noteworthy that I got them without using cheats. I don't remember exactly how I got them, but I played on version 0.6.0.
https://ibb.co/DCdBgw0
https://ibb.co/d2C7WdM
https://ibb.co/g9nbHvg
https://ibb.co/VMwz1QR
https://ibb.co/PFs3yx7
https://ibb.co/3BVS9Lg
Since this was necroposted already...
These blocks became canonized as smooth stone blocks in 1.14. They're a decent building block but expensive to obtain as you need to smelt cobblestone twice, or use silk touch on stone and then smelt once. I mostly relegate smooth stone to its crafting uses like armour stands and blast furnaces, and use smooth andesite or diorite instead.