Emohawk - Polymorph II - S6-E4
Revealing mistake: When the crew get hit by the gas at The End of the episode, you can see that they are slightly moving. (00:27:30)
Rimmerworld - S6-E5
Revealing mistake: When the Cat says 'All in all a hundred per cent successful trip' you can see Lister mouth the line. (00:13:45)
Rimmerworld - S6-E5
Revealing mistake: When the Cat says 'Form an orderly queue behind the gunsight' you can see Lister mouth the line. (00:15:40)
Rimmerworld - S6-E5
Revealing mistake: When Rimmer kisses the female Rimmer, the scar on his cheek disappears. (00:22:30)

Out Of Time - S6-E6
Revealing mistake: When the crew go through the unreality pocket that makes Starbug disappear around them, part of the Cat's face disappears into the background. (00:12:05)

Out Of Time - S6-E6
Revealing mistake: When the crew wake up from stasis, there is a model shot of Starbug flying towards the epicentre. You can see the legs of Starbug partially disappear as it gets closer to the ship. (00:12:45)






Chosen answer: In-universe, after leaving Red Dwarf after his first appearance, Kryten managed to crash Lister's space-bike into an asteroid. Lister found his remains and decided to rebuild him, however, due to the high level of damage and Lister's questionable repair skills, he was unable to recreate Kryten exactly, leading to changes in appearance, personality and accent. In reality, the original actor wasn't available, coupled with presumably practical concerns about one-off makeup as opposed to makeup for a regular cast member, so some visual changes were made.
Tailkinker ★