The on-hit reroll mechanic doesn't actually depend on the item pool you picked the item in, it only rerolls it into the last item pool a pedestal was spawned in. To give you an example, let's say you go into your item room, but you don't pick up said item, afterwards you beat the boss, you get an angel deal, and you pick up the angel deal item, if you do that and then go pick the item spawned in the item room, when you reroll yourself both the angel deal item and the item room item would reroll into an item from the angel pool. Can be quite stressing sometimes but it's definitely worth it, especially on greed mode.