Example and recreation:
I have base armor of 6 points and 2 identical diamond swords in inventory, each gives +4 armor in main hand and +6 armor in off hand.

Incorrect behavior #1:
Holding one sword in off hand and switching to another in main hand only applies attributes from main hand, forgetting attributes from off hand.

Incorrect behavior #2:
Attributes from off hand remain ignored when switching item in main hand.

Incorrect behavior #3:
Attributes from item in main hand being ignored when using fast swap button to place that item from off hand to main hand.

(Аffects any attribute modifier applied to items, not only armor)