Efficiency Enchantment not working on Diamond Shovel

What I expected to happen was"
I was digging out dirt and expected it to dig fast.

What actually happened was:
My diamond shovel that has Efficiency 5 on it dug the dirt/grass as fast as it would without Efficiency.

Steps to Reproduce:
1. Put Efficiency 4 or 5 on a diamond shovel
2. Dig out dirt/sand/gravel