So I've been watching a few tutorials and they've been able to place items or other full blocks directly on top of the slabs. Particularly if that slab is blacked on the lower half of a normal 1 meter block. I am unable to do that with mine. Whenever I try there is a gap between the slab and the item I place on top of it. It's as if the full block is actually there but only part of it is invisible. I've tried playing with settings and what not but I have not been successful.