Other mistake: At the start of "Backwards", there is a spoof "Star Wars" type caption, which spools up the screen very quickly. Too quickly to be read in fact...which may explain why few people have noticed that the last line of the caption "And now the Story Continuums..." is written TWICE
Other mistake: Kryten places Rimmer's light bee on the floor, then begins the process of reinitialising him. As the process finishes and Rimmer looks at Lister (who looks away), the light bee, which should be hovering within his torso projecting his image, is still visible on the floor between his feet.
Other mistake: At the start of Rimmer's exam, the invigilator orders the students to "turn over their papers and start". Rimmer reads one side of the paper, then turns it over to read another question. The back of the paper should have been blank as otherwise there would be no point asking the students to keep the papers face down before reading the questions.
Other mistake: When Lister reads Rimmer's diary, he reads the first entry, then his aunt's birthday in July and then the entry for Gazpacho Soup Day in November. Each time he looks for the next entry he flicks though the pages, yet every time he reads, it is from the start of the diary.
Other mistake: The tax letter and Rimmer's mother's letter are both already opened before Lister takes the letters out. As there is no one else aboard Red Dwarf, the letters would not have been checked by anyone so they should still be sealed. Also, not all of the letters are already open, just the two that Rimmer receives.