Continuity mistake: When Barf and Lone Star are rescuing Dot and the princess for the first time (from the Mercedes), they position their ship over the Mercedes but facing the other way (ie. facing Spaceball 1). However, in the interior shots showing Lone Star in the cockpit, the view is just clear space. Spaceball 1 is a gigantic ship, and they are very close to it (as well as angled slightly up to it), together with Spaceball 1's "mouth" being open which makes the ship even bigger vertically. It should block their entire view, but it's not seen at all.
Continuity mistake: When Lone Starr and Barf are at the diner after returning Princess Vespa to her father's castle, you see a creature burst out of a man's stomach. The creature then puts a hat on its forehead and begins to sing while walking along the countertop. But later, just before the creature exits, the hat is on the middle of its head.
Revealing mistake: When Pizza the Hutt is telling our heroes that they owe him money, watch his mouth. You can see the actor's real mouth appear a couple of times through the whole speech. The actor's chin is covered in the special effect pizza stuff, but you can still see his very human mouth every so often through this segment.
Continuity mistake: When Colonel Sanders and Dark Helmet meet to discuss Vespa's disappearance, Dark Helmet looks into the periscope and sees Lone Star's ship right behind them. But when they show the periscope Dark Helmet is using there is no view from the other side. How can he see from the other side of the periscope with no window there?
Continuity mistake: In the scene where Lone Starr is lifting the Yogurt statue with the Schwartz, when Barf walks in, Lone Starr drops his hand. But in the next shot when the statue falls, Lone Starr is still holding his hand up until the statue actually falls and then he drops his hand again. (00:49:25)
Continuity mistake: After Lone Star and Barf drop the giant hair dryer, they lift up the empty case. In the "Instant video Cassette" of the movie, Lone Star and Barf are lifting the case, but the hair dryer is missing.
Revealing mistake: When Vespa starts shooting at the guards on the platform, the one on the end flips over when shot, and you can see him bend over after he's shot to prepare himself for the stunt.
Continuity mistake: In the desert when we first see Lone Star and Barf carrying the luggage, Barf has two bags basically under his arms, with the straps over his shoulders. In the next shot the smaller bag has shifted over almost in front of him and the strap has dropped around his arm and chest.