When using efficiency diamond axe it mines slabs to fast.

When digging any kind of half slab (stone, quartz, stonebrick) using a diamond axe with an efficiency enchant it will mine it faster than it should.

Steps to Reproduce:
1. Get a diamond axe with any efficiency enchant.
2. Place down any kind of slab that isn't wood
3. Dig the slab with the axe.