In the episode where the mother dies, her son is talking to her and she's sitting down. Her hair is parted on the left. It cuts to the son, then back, and the part is on the right. It keeps changing, left, right, and it's a close up shot and really obvious.
The reason for this is because the episode was shot after Nancy Marchand (Livia Soprano) passed away. They had to use old shots of her & "insert" them into the show after the filming was done so they took the clips from different episodes.