Revealing mistake: When Tim gives Jill the framed photo of the two of them on their way to the Doobie Brothers concert, you can tell Tim has just been photoshopped into an existing picture of Patricia Richardson, as he is slightly out of focus despite the fact that they are standing next to each other. (00:13:24)
Continuity mistake: The conversation Tim and the others have at the hardware store becomes a lot different when Jill sees the (supposedly) same conversation on videotape. First of all, Tim's remark the "Jill's speech was so boring" has become "Jill's speech was so DULL". Secondly, Eddie's entire tale on how his wife wanted to change the fabric in the sun room is missing from the tape. And third, when Tim is talking about Jill's psychology studies, the expression "these terms" has become "these USELESS terms".
Other mistake: When Tim and Wilson are talking about The Beach Boys song lyrics, Wilson says he wrote a book called 'The Psycho-Physiological Indices of Amorous Connections Among Termites of the Southwest' that sold four copies. In an earlier episode called Wilson's Girlfriend, the woman Wilson dates also says she wrote the same book with the same number of copies sold.
Continuity mistake: When Jill is standing up to the other woman at Mark's karate class, she asks her "Will you stop calling my son 'Stick Boy'?" As the other woman replies "Then feed him something", her hands are on her hips, but when the angle changes, she has her right hand on her chest, with no time to move her hands between shots.
Continuity mistake: After Tim smashes Al's display cabinet, it cuts to Tim, then back to the workbench and the wrecked cabinet. The pieces of china and the pieces of wood on the bench differ in the two shots. In the first shot, there are two whole teacups, one whole plate and a bit of a shelf on the bench (the shelf is on the right side of the screen), in the second shot we see a broken tea cup, one broken and one whole plate, and the piece of shelf has disappeared.
Continuity mistake: At the beginning of episode 4.10, "Ye Olde Shoppe Teacher", Tim's lopsided toolbox that he made turns 180 degrees as Jill pushes it away. As Jill and Tim are talking, it turns back. Then it turns 180 degrees again just before Tim briefly leaves the room.