Shovel bug

I enchanted my diamond shovel in level 30, and got unbreaking 3 and efficiency 4 just as I hoped. I went to go digging out a mountain, when I found out that the efficiency on the shovel has no effect. I went to a test world to find out if that was right, and I was. A normal diamond shovel did the exactly same thing as a diamond shovel with efficiency 5. Thank you.