In some scenes, Uncle Buck's car has a red "Tow Away" tag attached to the windshield and in others it does not. At 01:13:16 and 01:22:57 there are red and white papers on the dashboard seen through the front windshield. At 01:15:41 there is a black on red sheet reading "ABANDONED AUTO" on the dashboard.
When Uncle Buck is in the bowling alley with Tia, Miles, and Maisey - "Pal" has already come to sit next to Tia - but in the long shot of Uncle Buck helping Maisey bowl, Tia is clearly sitting alone on the bench behind the lane.
When Miles unpacks the lunch that Uncle Buck has made for him and asks the boy to his right "Would you like to talk about a possible lunch trade?" (27:51 to 28:10), the scene cuts to an overhead shot (28:11 to 28:12) of the three boys at his table propelling their chairs backwards across the room. The overhead cut has numerous continuity errors. At 28:11, (1) Miles is still unpacking his lunch so his hand is back in the lunch bag and he is missing the canned sardines and two plastic bags, (2) the boy to Miles' right is wearing a solid purple shirt rather than a blue shirt with black stripes, and (3) the sandwich in the right hand of the boy to Miles' right has been replaced with a bag of Fritos.
Buck's car backfires every time when the car is stopped. But for some scenes, the car never backfires.
1. When Buck arrives at the Russell's house for the first time.
2. When Buck stops at a stop light looking for the party Tia is at.
3. When Buck finds Tia walking down the street after the party.
When the teacher is asking the class a question and Maisy raises her hand (at around 58 mins), a girl in the background can be seen with a book and a box of crayons on her desk. In the next shot of Maisy, the crayons and book are missing (58:01).
When Buck is smoking near the fireplace on the couch the length of his cigar ash changes (01:08:34 medium, 01:09:22 long, 01:09:49 short). This is also an issue while Buck is looking at the wedding photos before (28:28) and after (28:38) he pulls out the folded photo.
When Uncle Buck is drinking on the couch, at first, in a frontal shot (at around 1h 08 mins), the label on his beer bottle is to his right. In the next cut, from behind him, the label is on his left side (01:08:36). Then, when viewed again from the front, the label is again on his right side (01:08:42).
At the beginning of the bowling alley scene, Uncle Buck rolls a ball in unison with a man on the next lane (at around 5 mins). We then see the ball knock over all the pins, but when they cut back to Buck celebrating his strike, the man next to him is rolling another ball already (at around 10 mins).
When Buck takes the cat back out of the house, as he walks through the doorway you can see a person standing behind the door waiting to close it (at 01:00:33 seen through the slit between the door and the frame at the hinges). This person is a lot taller than a six year old. The form is also seen through the slit (and moves) from 01:00:17 to 01:00:27 when Buck first brings the cat into the house. The scene from 01:00:17 to 01:00:48 is shot in a single take. The intent of the film is that the children close the door because the porch light is shut off at 01:00:39 and the children giggle about it, but since children have restricted work hours and this scene does not require them to be on-camera, it would make sense that it was shot when no children were on the set.
When the next door neighbor comes over to entertain Uncle Buck, we see a tone arm drop on the 45 RPM record... notice the label.. it's the old UNI label (70s Neil Diamond, late 60s Strawberry Alarm Clock) but, when the record start playing, it's the Beau Brummels' classic "Laugh, Laugh" that we hear, a song that was NEVER released (or for that matter re-released) on the UNI label.
During the shot right after Buck makes his long cough while on the phone with Bob, it appears that there is a person in bed laying beside Buck (at 10:18 in a wider shot with the foot of the bed facing the camera), and Buck looks directly at this person when he turns on the Clapper, as if to ascertain whether she woke up. Later, as he's packing his things, he does so with no indication that anyone else is there (i.e., no tiptoeing around), and he subsequently calls Chanice, which confirms that she is at her own home.
In the early scene where Bob calls Buck to ask him to house-sit while he and Cindy are away, Buck's overnight "guest" is obviously a blow-up sex doll, not a living breathing female companion. Buck even says "I just used your Christmas present", glancing at the inanimate object beside him.