???!!!DUUUUHHHH!!!! - I kept wondering why some of my villagers work in fast forward. I've made the potion but the results didn't register.
One day one of my villagers found a green pearl and ground it into powder and made a potion from it. It has the same result. To be honest, that's when I started paying attention and trying to work it out but I had not made the potion for so long that it didn't click.