Deliberate mistake: Proctor and Harris were surprised when they walked into the Blue Oyster and found out it wasn't a restaurant, but in Police Academy 2, Proctor apparently knew not only the bar, but the address as well.
Police Academy 4: Citizens on Patrol (1987)
1 deliberate mistake - chronological order
Starring: Steve Guttenberg, G.W. Bailey, Bubba Smith, David Graf, Michael Winslow, Bobcat Goldthwait
Continuity mistake: At the end of the movie when Tackleberry glides down the balloon you can see that the color/shape of the balloon changes between the closeup and far off shots.
Captain Harris: Don't touch those! Don't you ever touch my balls without asking!
Trivia: This was the last film in the Police Academy series to feature Steve Guttenberg as Carey Mahoney, the main protagonist of the series up to this point.