Factual error: When Edgar the Butler directs the Old Solicitor upstairs they have a bit of a struggle with the steps. Before this you saw the Solicitor arriving in his car and this gave you an impression how high the first floor of the building of the Old Spinster was. Judging by the amount of steps on the stairs the pair would have ended up on the roof.
Factual error: At the very beginning when the family are in the cart being pulled by Frou-Frou, the way Frou-Frou is trotting is completely wrong compared to how a real horse trots. When she is moving it is front and back right, and then front and back left. It should actually be front right and back left and vice-versa.
Chosen answer: It is the style of the artwork. Similarly, it is not a mistake that each individual hair is not drawn, the eyes are not really proportional to the head, etc.
Myridon