Watch the following Thay's video from 4:42 to 5:52.
"Negative seeds (karma) will always be there even after you have become a Buddha. Buddha is not a person who does not have the negative seeds. Buddha is someone who knows how to protect himself so that negative seeds in him not to be watered by himself and by others. And Buddha is someone who knows how to allow his good seeds to be watered every day so that happiness and compassion can grow every day. So, I do have a seed of depression. And all persons have a seed of depression. But if you know the practice of right diligence, you will be okay. And the other kinds of seeds will have no chance to manifest and take us away."
Above shows that our past negative karma will not be eliminated upon enlightenment. So, our past negative karma may cause the negative impact even after enlightenment if we don't protect ourselves. But enlightened persons know the selective watering method to prevent the negative impact from occurring.