Why Can't We Be Friends? - S8-E5
Factual error: When the guys are on the Graviton, you can tell they're spinning clockwise, or to their left. That means everything should be pushed in the opposite direction, but one girl's hair is flowing to her left when it should be flowing to her right.
Blood Crieth Unto Heaven - S8-E10
Continuity mistake: When Stan and Francine are first in the kitchen, a record player is briefly seen to the right of the screen. However, when Stan returns to the kitchen after all his dad's items have been put in the bag there is no sign of the record player in the other room. (00:03:15 - 00:03:55)
Adventures in Hayleysitting - S8-E6
Other mistake: When Hayley is chasing Steve and his friends in her car, after Steve gets on the bus, Hayley turns around a corner to follow it. When this happens, the license plate on Hayley's car has nothing written on it.
Chosen answer: It is just the decision of the creators to do so.
MasterOfAll