Continuity mistake: Steve receives a Rowflux and five containers of protein powder. He takes one of the containers leaving only four still on the floor. In a subsequent scene, Steve is still holding the container but now five containers can be seen behind him, giving him six containers altogether.
Cock of the Sleepwalk - S9-E11
Continuity mistake: After Stan says "Fired?!" and the camera goes back to Bullock, the word IHOP appears on the board behind them. (00:13:45)
Other mistake: When Francine gives the family gifts, Stan writes "How did you pay for this?" on his board. Francine replies "Well, money, of course" to which Stan writes another sentence on his board. He starts writing without clearing the board, yet when he turns the board back to show the sentence "Is that true, Steve?", the original "How did you pay for this?" isn't visible on the board, despite not clearing it. (00:12:00)
Character mistake: When Francine calls Stan to tell him Hayley is in rehab, he later asks her whose car she crashed, when Francine had never said that a car had been crashed to begin with.
Continuity mistake: Stan hears Francine's parents at the door, and Klaus is in front of him with a bowl of nachos to the left of Klaus. In a few shots, Klaus's bowl and the nachos switch spots.
Chosen answer: It is just the decision of the creators to do so.
MasterOfAll