Visible crew/equipment: In the scene where Maxine comes out of the bathroom and yells "Jack" a microphone appears for a second at the top of the screen. (00:25:05)
Continuity mistake: The kitchen changes from episode to episode, when viewed from the living room. If the set is going to be used the full kitchen is visible when viewed. But if it is not being used, often the set is pushed closer together. This is most evident when an actor is coming out of the kitchen the stove and the attached cupboards are practically at the door, providing just a bit of space for the actor to stand before making their entrance. Other times a wall is simply pushed up beside the door with the kitchen wall paper on it to appear to have continuity. This is only seen when the shot allows the kitchen set to be obscured.
Plot hole: Janet and Chrissy accuse Jack of making the fake BBQ telegram. However, Jack was at The Apartment the whole time, never left once until after he found out Lori was the one who made the telegram. If it was Jack who made the fake telegram, he would have had to leave The Apartment to do that.
Suggested correction: True, there's no logical way that Jack could have sent the telegram. But Janet and Chrissy were upset about it - when someone's upset, they don't always think in a logical way.
Or he could've called Larry and had him set it up but I don't think he ever used the phone to call anyone.
Diamond Jack - S7-E3
Character mistake: At the roller skating rink, Jack looks at the menu on the wall in the snack bar while ordering two sodas and says "What are they... 50 cents a piece?" However, only food items and candy are listed on the menu and drinks are not mentioned at all. How did he know the price?
Character mistake: The undercover cop who first mistook Chrissy for a hooker, first admits he was wrong about the way he judged her. Then upon finding out that Jack lived with her and Janet, he came on to her instantly thinking she's "easy" once again. However, the cop was already informed by Mr. Roper that Jack was gay at this point, so the fact that a "gay" man living with women should not have changed the cop's mind of how to view Chrissy the way he did.
Continuity mistake: In this episode, Larry is a really poor sounding singer, but in the episode "Strangers in the Night (6-12) " in the previous season, Larry sang perfectly without any problems.
Character mistake: When Jack tells Mr. Furley his brother is in town (before mentioning it was a "twin" brother who Jack made up), Mr. Furley gave a puzzled look and said "Your brother?" which appeared as if he didn't know Jack had a brother. However, in the previous season, Mr. Furley briefly met Jack's brother Lee, so he already should have known Jack had a brother (even if were to turn out to be a different brother).
Jack Goes to the Dentist - S7-E2
Character mistake: When the dentist is putting cotton in Jack's mouth he neglects to put on rubber gloves first as dentists are supposed to do before any dental work.
Good Old Reliable Janet - S3-E2
Character mistake: At one point in this episode, Jack is chatting with Larry about the nude beach and in frustration says "all the best looking girls were wearing moth-eaten blankets" right in front of Mr. Roper as well as showing interest in seeing Janet without her clothes also in front of Mr. Roper. Jack is supposed to pretend he's gay when Mr. Roper's around him. Roper luckily didn't pick up on it this one episode either time (rather showing concern for his wife).
The Not-So-Great Imposter - S5-E9
Revealing mistake: The kitchen of the husband with the cheating wife is the same kitchen used for Chrissy's parents house in Fresno at the very end of the next episode end of episode "Jack's Other Mother" (S05E10).
Revealing mistake: When Jack and Janet are in the entry looking around for burglars, their voices are over-amplified, indicating they are in a sound studio.
Jack in the Flower Shop - S2-E19
Revealing mistake: Once Jack arrives home from his first day, Janet follows shortly behind him with her arms full of groceries. She hands the bag to Chrissy but watch at the bottom of the bag - it starts to come apart and Chrissy grabs the bottom of it and holds it together. The end sight gag is that when Jack storms out, and Janet storms off, Chrissy then goes to go to the kitchen, and the groceries fall out of the bag at the bottom - but it's because then she's holding the bag then around the center.
Will the Real Jack Tripper . . . - S2-E21
Character mistake: When the angry father comes to the door at the end of the episode looking for Jack, Mr. Roper opens the door and after the father asks "Jack Tripper?", Mr. Roper responds "Yes" and then gets chased around by the father assuming Roper is Jack. Why would Roper respond "Yes" anyway? He's not Jack and would never say he was - just scripted as a way to get chased around but in a real situation, he would have no reason to answer that way.
She Loves Me, She Loves Me Not - S8-E2
Visible crew/equipment: When Larry hops out of the canoe over the magazine panic, saying, "I gotta see Jack," the boom is quite visible at the left as the camera pulls back.
Jack Goes the Distance - S7-E16
Continuity mistake: In many earlier episodes, Jack always mentions he was a boxing champion in the navy. But in this episode, Jack admits he lost every fight in the navy.
Plot hole: At the party, when Jack tries to suddenly stop many guests from eating his tainted cake, he knocks away the cake from many people to prevent them from eating it - but at least two minutes or so have gone by since the guests were given the cake slices so most likely, many (if not all) the guests would have tried the cake within those two minutes. And yet somehow Mr. Roper was the only one who is revealed to have actually tried the cake in all that time.
Grandma Jack - S8-E7
Character mistake: Jack says to Larry (upon finding out "Grandma" Tripper won the contest), "You want me to dress as a woman?" as if he never did that before and thought the whole idea was crazy - but earlier in the series he dressed as Chrissy in full drag so he's not new to the idea like he made it sound. Larry also dressed as a woman in an earlier episode as well (just for the record).
Helen's Job - S2-E13
Visible crew/equipment: Janet stops Helen from leaving, says she can't handle seeing her beat. After Helen's speech about winning the war, as the camera zooms out, a piece of set equipment is briefly visible at the top of the screen. (00:16:55)
Ground Rules - S2-E1
Visible crew/equipment: Shadows of the boom and a crew person moving reflect off Jack's hair as he's talking with Janet in the kitchen.
Visible crew/equipment: A crew person's arm or equipment can be seen at the far right of the screen, when Mr Roper asks Jack for some baked beans, after the opening credits. (00:01:10)
