>>56974438It makes sense to me. Pickup drops the item directly into the Pokemon's hold item slot, not your bag. No it doesn't matter what you have in the bag, since you could yourself just give it one of your max'd out items to hold, get another one to replace it in the bag, and functionally achieve the same thing as the pickup drop.
Hell, even if it did drop it into your bag, it'd make sense for it to just not drop anything on that roll. I don't particularly see the logic of it defaulting to another item in that case. You rolled a specific item, and that roll is always independent of what you already have.