Plot hole: When the castle is about to blast off, Brad and Janet abandon Dr. Scott's wheelchair at the door of the castle and carry/drag him across the porch and down the steps. After the blast off, Brad, Janet, and Dr. Scott are on the grass and have been blown some distance apart from each other (in the UK version, there's another song where Brad and Janet crawl toward Dr. Scott so they are blown farther apart than shown in the US version). It seems extremely unlikely that the remains of Dr. Scott's wheelchair just happened to fly from the doorway to land directly under him during the blast. Brad and Janet can barely crawl so they didn't move him or it. (01:34:10)
Plot hole: When Vic steals the food from the group in the desert, we see he's been standing about 100 yards from them, all the while they've been digging. This is filmed on the Bonneville Salt Flats, with completely flat ground for miles around. Did the group just not notice a guy (and a dog) standing that close to them? Did they not think of protecting their site with a guard (there are 2 kids and a cripple there, but even they don't notice Vic until he's just ten yards away, running towards them)? As well, the crime 'boss' character allows Vic to get away and does not chase him - he even laughs that someone has the guts to try it. Food is very precious in this world, and nobody would likely allow this theft, much less a criminal boss. (00:15:45)