Wood Slabs can only be taken with a pickaxe

Wooden slabs act entirely like a stone slab. It can only be taken with a pick and when you walk on it, it even sounds like stone.

What I expected to happen was...:
To be able to take wooden slabs with an axe, not a pick.

What actually happened was...:
They can only be taken with a pick.

Steps to Reproduce:
1. Place a wooden slab and try it with an axe.
2. It will be destroyed and not give you the slab back.
3. Try the same thing with a pickaxe.