Continuity mistake: In the opening credits of the first season of The Odd Couple, Felix is moving in "with his childhood friend", Oscar. In a subsequent season, a storyline does a flashback to say that Felix and Oscar met when they were both jurors at a trial. Soon after, they cut the word "childhood" on most of the openings after people called the station to mention the mistake.
Continuity mistake: When Felix is shown being thrown out of his apartment and entering Oscar's apartment, the suitcase under his arm is a different color than when he is shown on the street on the way to Oscar's apartment.