Durability goes down when PVP off.

When PVP is disabled because of the scoreboard Team 'friendlyfire' option, the durability of the tool still goes down when you hit someone.

What I expected to happen:
When I hit someone with my sword on my team, it doesn't damage him, and doesn't damage my sword.

What happened:
It didn't damage him, but the durability of the sword lowered.

How to reproduce:
1. Go both in survival mode
2. Create a team ( /scoreboard teams add TeamName )
3. Set Friendly Fire to false ( /scoreboard teams option TeamName friendlyfire false )
4. Both join the same team
5. Get a sword (type doesn't matter)
6. Hit the other one a few times, and see the durability go down.