So I was wondering.. a Stair or bottom slab is not a valid spawn block for mobs. Although a top slab is. So is an upside down stair also a a valid spawn block for mobs?Like a top slab, it produces a full flat surface along the top surface of that block. But I have never tested this. And it would be useful to know.Anyone know for sure?Please don't post a guess... give a reason.