When two slabs are stacked on one another to make it appear as if its one whole block, they act as if they're one block when being mined, but drop as two. Because of this, if a slab is misplaced, both slabs must be mined to get the one.
MCPE-2047
Mining stacked slabs acts as if one block
Resolved
Works As Intended
0
This is Working as intended.
When you place the second slab on top of the first slab (Data value 44), both slabs are converted to one double slab Data value 43).
When you mine the block, you mine the one double slab block, since there aren't two slabs anymore.