Trying to find the right thread, but i think i've heard of this before.
It came up in discussions about the gear 'dupe' if you win a battle vs a fief.
It wasnt clear if this happened in every successful siege defense or just some, but it's looking like that it's all siege defenses (and we havent noticed yet cos most sieges have been vs AI).
Also heard some rumours that the gear you used up returns to it's original state, whilst you fail to loot anything from the attacker. Is this something you've observed?