I noticed it mainly with toxic ingredients not applying the reduction and increase of toxicity.
The one i remembered clearly was adding an eye to add a bit of toxicity, but it adding 0. Maybe it happend due to me adding milk first and it going into the negative, but i'd assume you clamped it 0 to avoid it.
Might also be that is purely visual.
In regards to what time, i believe it was on one of the last day or two, well into the game.