This isn't really for explaining the mechanics, but moreso asking about this. From what I understand, when you place a Power Item that you use to train for on a Pokémon you wish to breed, the stat's IV for which the Power Item is for should pass down guarenteed. Now this has not been the case on. On multiple occasions, I've had a Power Item for a 31 IV, and it hasn't passed down. Has this happened to anyone else? Does anyone have an explanation for this?

EDIT: I found this from Bulbapedia. I'm saddened at myself for not finding this before. I'm locking the thread now. "In Pokémon HeartGold and SoulSilver onward, if they are held by either parent in the Pokémon Day Care, that parent has a 50% likelihood of passing down its IV in that respective stat; HP for Power Weight, Attack for Power Bracer, and so on."