A running gag throughout the movie is that whenever Dark Helmet has his helmet closed, his vocal tone is much deeper than it is when his helmet is opened. In the scene where he is searching for Lone Star & the gang with the binoculars however, he complains to Colonel Sandurz about "always preparing to do something and not just doing it" and when he says that, his voice is normal-toned, even though his helmet is closed.
When Dark Helmet and Sandurz are watching the tape of Spaceballs, the scrolling words shown at the beginning of the tape do not match what was actually shown at the beginning of the movie. (On the tape, the letters are all capitals, but are upper and lower case in the movie's beginning.)
In the cave, when Yogurt first appears, a door opens in the base of his statue, he walks out, and the door closes behind him. In the very next shot, the door is open again, Yogurt walks out again, and the door closes behind him again. (DVD version)
After Lone Starr sprays shaving cream in the guard's face, he gives him the "Vulcan Nerve Pinch" to knock him out. As the guard falls, he knocks Lone Starr's ring off his finger. In the next shot, Lone Starr has the ring on again.
Just before Spaceball-1 rendezvous with Princess Vespa's Mercedes, the icons for the two ships (on Spaceball-1's teledar screen) are drawn and moved as though the two ships are approaching nearly head-on. When the camera cuts to an outside shot, Spaceball-1 is instead shown trying to catch up with and overtake Vespa's ship.
When Lone Starr and Barf jam Spaceball 1, Michael Winslow calls over Colonel Sandurz and Dark Helmet. Right before Dark Helmet says "raspberry", Michael Winslow puts his hand over his mouth. In the next shot his hand isn't there anymore.
When Barf interrupts Lone Starr's attempt to lift the statue, Lone Starr lowers his hand, which causes him to drop the statue. In the next shot showing the statue on Barf's foot, Lone Starr's hand is raised again, just for a second.
When Barf and Lone Star rescue the princess and Dot Matrix from being brought into Dark Helmet's ship, they can breathe in space. This would seem to spoil the motive for stealing Druidia's air supply. However, it is possible that the futuristic technology allowed a force-field to contain a bubble of air around the two vessels.
The scene where Lone Starr has the Yogurt statue in the air, Barf walks over to the statue and asks "Hey, boss. How'd you do that?" Lone Starr lets the statue drop to the ground and as the statue hits the ground, the head on the statue shakes, showing that the statue is not real.
In the hover car scene, when Lord Helmet is looking through the binoculars you can clearly see the hover car is half a prop with a piece of glass or a mirror covering the bottom section. You can distinctly see a difference in the sand under the hover car, as opposed to the surrounding area.
Just after Dark Helmet throws Lone Star's Schwartz ring down the grating, Lone Star gets up and swirls to face Dark Helmet, then starts backing toward the door. When he does, you can clearly see his face for a few seconds, and it is that of the stunt double, not Bill Pullman.
Just after the Winnebago exits "hyper-active", the ship's engines lose power. Barf clearly points out on the fuel gauge that this is "because we're outta gas". When the camera cuts to a shot from behind the ship, the main engines appear to be running at full blast. They should be off or at least sputtering.
When they first meet Yogurt, a closeup of the statue is shown, with smoke moving in a very slow and choppy manner relative to the other shots in this scene. The film is playing at a slower rate than usual.
When Commanderette Zircon calls Skroob in the bathroom, her image and that of her surroundings is not properly perspective-shifted to match the camera angle and perspective of the wall on which her transmission appears.
When Lone Starr's Winnebago is overtaken by Spaceball One, the plaid pattern trail of Spaceball One is moving in the view through the windshield. Then the camera switches to show Lone Starr and Barf and the plaid light pattern reflecting off the back of the cabin is static.