Describe the bug
I noticed this while playing with the new caestus weapons, dual-wielding them would drain only the main hand's durability. I tested this with other weapons, seems like any weapon held in offhand doesn't consume their durability.

To Reproduce
Steps to reproduce the behavior:
Equip a weapon in offhand
Deal damage to mobs to reduce it's durability.
It remains at full durability.

Expected behavior
It should consume durability.

Info (please complete the following information):

• Modpack Version: 2.75.1
• Server or Singleplayer: Singleplayer
• Version the world was created on: 2.74