What's the mechanism behind item morale?

[goldenpath]

What causes the morale of an item goes down? At first I thought all item morale goes down after each battle, but that's not true. I compared the morale of 2 items before and after a deadly fight, only one lowered and other one unchanged.

I've also read about the item morale is related to the race and the enemy race that you fought (so for an Human weapon, its morale will go down if you kill bunch of human packs) but after testing its not true either...hmm