Continuity mistake: When the house first becomes detaches from its foundation and becomes airborne, Russell is nowhere to be seen, although every angle of the house is shown, including underneath, the front porch and the back porch. He knocks on the door and tells Carl he chased a "snipe" under the porch - but he cannot be seen after liftoff and prior to knocking.
Other mistake: Shortly after the house takes off for the first time, in a scene where part of the city can be seen that includes various buildings and houses, the shadow of Carl's house and the balloons can be seen on the ground. At first glance it looks OK, but the angle of the shadows of objects on the ground is completely different from the shadow projected by the house. The buildings on the ground are projecting a shadow to the left, indicating that the sun is low to the right. However Carl's house shadow indicates a light source from behind the camera which is about perpendicular to the shadows on the ground. To be technically correct in this shot, all shadows must point away from the camera and the sun should be located behind the camera if the house's shadow is to be seen in the shot.
Continuity mistake: When the house first lifts off, the bottom step of the front porch becomes detached at one end and sags. In the next shot when the house brushes the top of the transport van, the step is undamaged and isn't sagging.
Continuity mistake: When Russell lifts off from the roof of the house with Carl's leaf blower, it is obviously gasoline-powered because he pulls the starter rope and we see smoke. Once inside the blimp, Russell uses the blower on the bulldog and he starts it without pulling the rope.
Continuity mistake: When Mr. Carl notices his mail he holds the stick in his left hand and reaches near the mailbox. He places the walking stick to his left, the next shot after he picks up the mail and comes back, the stick is not found, but in the next shot it's found to Mr. Carl's right side when he speaks to the man in black suit.
Other mistake: After Carl and Russell meet with Cumulonimbus cloud Carl takes a nap and we find that Russell wakes him up, after that we see that Carl goes and peeps out of the window he places his walking stick near to him and facing him, the next to next shot we see that its moved and is facing opposite to him. even though the camera is moved a bit its not possible for the stick to rotate so much and moved.
Continuity mistake: When Ellie first shows Carl her Adventure Book, page 1 is a map of South America, page 2 is the library-book picture of the falls, and page 3 is the page marked Stuff I'm Going to Do. In the next shot, we see five pages precede the Stuff I'm Going to Do page.
Continuity mistake: After being tied up and rescued by Carl, Russell falls backwards off the front porch and is saved by the garden hose. In the first shot, Russell is standing on the nozzle hanging on, but when he is dragged across the windshield of the blimp, he is hanging on with his hands. The next shot in which we see him, he is back in a standing position.
Continuity mistake: After Muntz ties Russell to the chair and opens the ramp, there is a fast sweeping exterior shot of the blimp's underside from front to rear, and the ramp is opening toward the front. In all other scenes of the ramp, it opens toward the rear.
Continuity mistake: The fence gate on Carl's house has some continuity issues. When we see him arriving home after Ellie's funeral, the gate is open toward the inside. The width of the opening looks to be fairly large, around 46 inches based on the total approximate widths of the planks on the house porch which is shown the same width as the gate opening (10 planks at least 4 inches wide and one plank at least 6 inches wide). The next day when Carl gets the mail, the gate opens toward the street and stops at the post - can't be opened to the inside. When the construction worker finishes his interaction with Carl, we see the complete gate and it is much narrower than the funeral shot. It now has only 4 planks which look about 6 or 8 inches wide, so the width is about a foot less than the night before.
Continuity mistake: In the scene were Russell finds the lever to operate the house direction, he moves it first towards right, then to its left and again to its right and finally leaves it in the center and goes towards the window. But in the next shot, it's found positioning to its right.