I believe I can explain the bones ending up in the hair stockpile...
Short version:
Procedurally generated creature parts are implicitly added to a refuse stockpile, and can only be removed by first blocking all and then adding the stuff you want (which can be rather tedious for some cases).
Long version:
Before visitors were introduced all non dwarves were hauled to the refuse stockpile rather than the corpse one. Since corpses of sapients caused fear among the dwarves and immediate flight among merchants, I separated "refuse" consisting of bits from former sapients from the other refuse into a separate stockpile, kept out of view. However, some clowns are sapient, and ended up in the refuse stockpile. Only by blocking everything and then adding the things you want you can get them to end up in the right place. I have no reason to believe that logic has changed, even when all sapients were redirected to the corpse ('y') stockpile. I think you can keep FB remains out of your hair stockpile by blocking all, enabling hair, and then disabling the hair that can be spun. With this process you won't get any FB hair in that stockpile either (it would go to any refuse stockpile that hasn't blocked all).
As an aside, it can be noted that remains of reanimated former sapients are treated as refuse (and is not scary). "Naturally" butchered bones (resulting from decay of arms and legs) from zombies can be used in crafting by dorfs, while bones from sapients can not (any longer: they could be used before the visitor introduction). Also note that zombie remains are non scary.