Arrows shot from a dispenser into a half slab can be picked up from far away.

When a dispenser shoots an arrow right into a half slab, the arrow can be picked up from far away.

What I expected to happen was...:
To pick up the arrow when right in front of the dispenser.

What actually happened was...:
I could pick up the arrow from 7 blocks away.

Steps to Reproduce:
1. Take a dispenser and fill it with some arrows
2. take redstone and button and hook it up to the dispenser
3. press the button and walk away from the dispenser.