/enchant glitch on multiplayer servers

When I did /enchant on my sword, it said; "Diamond Shovel cannot support that enchantment" even though I was enchanting my sword.

What I expected to happen was...:
I thought it was going to enchant my sword

What actually happened was...:
It enchanted my shovel with an enchantment it couldn't handle

Steps to Reproduce:
1. Get a diamond sword, followed by a diamond shovel (specifically enchanted with efficiency 2)
2. Make sure you're in a multiplayer server, and alone
3. Put your sword in the 6th slot, and your shovel in the seventh.

4. Now try to enchant your sword with sharpness 3