Other mistake: In outside shots the front door is on the extreme right. Shots from inside the house show the living room on the left and the door in a central position.
Mammary Lane - S5-E5
Continuity mistake: At the beginning of the episode, the establishing shot shows a bowling alley with a sign that reads Mar Lin Do Lanes. A few minutes later, Doug welcomes Denise on behalf of the family at Bowl-O-Rama. (00:04:10)
Character mistake: In the opening scene, Doug call Carrie "Kel" which is Deacon's wife. He calls her that when he's saying they should just get a new grill.
Continuity mistake: When Doug and Carrie are in the living room talking about Doug not going out with Kelly again, he has the phone in his hand, gets upset and throws the phone down. Then Carrie is going to call Kelly for Doug, and when she goes to pick up the phone, it's placed perfectly back on the hook when it should be hanging near the floor from the way Doug threw it.

Visible crew/equipment: Near the beginning when Doug comes into the kitchen and smashes the cake with the watermelon, you can see a stage light reflecting in the door window 3 times as it swings open. (00:00:10)
Queasy Rider - S2-E1
Other mistake: Arthur gives his CV to Doug at the start. You can see it's typed but both Doug and Arthur talk about it being in magic marker. (00:00:30)
Head First - S1-E6
Continuity mistake: During the poker game, Arthur teases Spence because he's a virgin, which is mentioned later when Doug tells Cariie, "He teased him about the virgin thing." But in one of the later episodes, it is mentioned that Spence had an affair and had sex with his Home Economics teacher when he was very young and had long hair.
Character mistake: When Carrie finds Tina, she mentions the "stuff" that Tina listens to at work, and Tina tells her that it's salsa. We know from previous episodes that Carrie likes salsa dancing, so shouldn't she know salsa music?
Other mistake: On the exterior front shots of the house you see the front door with three vertical windows. But on the interior shots it is just one window.
Revealing mistake: When they first drive to their class, we see the street lights behind them. When Carrie pulls over to pick up Spence, she turns the steering wheel, but the lights in the back don't turn. (00:07:45)
Visible crew/equipment: Stage lights can be seen reflecting off the fake apples in the table center-piece at the hotel. (00:02:25)
Continuity mistake: The box of Sgt Salty cereal alternates from open to closed between shots when Doug and Carrie are talking. (00:13:30)
Continuity mistake: When Doug, Carrie, Deacon and Kelly are at Coopers, the man in the blue shirt who is talking to the women sitting at the table behind them appears, disappears, walks off and then reappears again during this scene. (00:08:20 - 00:10:40)
Tank Heaven - S6-E21
Visible crew/equipment: When Doug and Carrie close the door after saying bye to the first couple, you can see camera lights and a boom mic moving in and out reflected in the window behind them. (00:06:10)

Continuity mistake: At the start Doug puts a drink down after taking the top off. Camera cuts and the lid is back on. (00:03:30)

Continuity mistake: When Deacon and Kirby are at Doug's the house over street is a mid terraced house in one shot, and an end terrace in another. (00:06:00)
Tank Heaven - S6-E21
Continuity mistake: In the scene where Danny has just taken the "nucleus" nacho chip, after Carrie walks in, the chip in Danny's hand keeps changing between shots, then disappears altogether almost instantly and his arms are folded when he begins his next line. (00:02:30 - 00:03:25)
Queasy Rider - S2-E1
Continuity mistake: When Arthur starts telling Doug about when he had a bike, you can see the tv gets switched off. However neither Doug or Arthur turn it off as both of their hands are in screen and the remote is on the table. (00:14:30)
Continuity mistake: In front shots of the house you see that the garage is in the front and opens to the street, but the garage door is behind the house entirely. It seems to open in a back alley or private entrance way. The way it is shown in establishing shots, it can not be open to the front street at the front of the house.
Suggested correction: Spence did have sex with the teacher, but the episode with the teasing at the poker game, Arthur and the guys don't know about her yet. Therefore, to their knowledge, Spence is a virgin, and for some reason, he decides not to defend himself with the teacher story.
The episode with them playing cards wasn't the only season 1 episode where Spence's virginity had come up. In season 1, episode 12, Carrie fixes Spence up with a coworker. When Richie and Doug tease him that they've already been together a month without sex they say: "Do you believe this guy?" "A month, huh?" Spence replies: "Yes a month! A month is not that long not to have had sex." To which Doug says: "Yeah, but if you add in the other 31 years, I'd think you'd be a little antsy." Also a little later in the conversation, when Doug tries to convince Spence that he and the girl have sex in his garage: "I'm just saying, if you wait too long, this opportunity could go bye-bye. Then it could be, hey, another 31 years before this opportunity comes again. It's pretty tough losing your virginity when you're 62." So Spence later already having lost his virginity in high school is a continuity error that they just overlooked and alas instances like these become apparent pretty often when you rewatch the show (like Carrie becoming an only Child, Arthur being said to be a great piano player in a season 1 episode while he can't play a single tune in a later season etc., etc).
Suggested correction: Spence was embarrassed about sleeping with the Home Ec. Teacher - which is why, in the high school reunion episode, he claims that he actually slept with his Spanish teacher. He also never called the Home Ec. Teacher after their "fling." Apparently he prefers to let the guys think he is a virgin.
Azalea