Continuity mistake: In the opening titles (for series 1-3), Stan runs outside and picks up a newspaper. He reads the headline and throws it back on the ground. But by the time Stan drives off, the newspaper has disappeared. (00:00:10)
Continuity mistake: The window partway up the Smith staircase vanishes after the first season.
Chosen answer: It is just the decision of the creators to do so.
MasterOfAll