Any stone slabs ontop of one another creates a double stone block

I opened up minecraft and saw there were some smooth double stone slab blocks in my world, after testing in previous versions and seeing that they were unavailable in recent versions I got confused and middle clicked on it and it gave me a stone brick half slab, I placed it down and it was as you would expect but then I put another on top of it and it turned into the smooth double stone slab. CTRL + Middle click won't give me the block either.

Upon further investigation I have found that it happens with every slab, not just the stone bricks.

More testing and it doesn't effect any wood slabs but all others.