A surprsingly interesting example comes from the PBS show Cyberchase, relating to one of the later seasons. At the end of a four part series with Hacker failing to take over Cyberspace with a transforming machine, the Cyber pal's friend Slider is seeing going home with his dad to attempt to find a cure for his disease. Now, this is significant, because one of the main plots in Cybechase has been trying to find Slider's missing father, and this episode appears to wrap it up.
What is strange is that, in the next episode Slider appears in, he's back to asking Hacker where he took his dad, as if the previous episode with him never happened! Worse, his dad never appears in the cartoon again, which makes this not just a case of a character disapearing for no reason, but a character disapearing from the show in a way that contradicts previous events!
This to me strikes as a huge mistake on the shows creators, even considering that it's only a PBS cartoon. I really don't understand why that happened, as you'd think they'd be able to catch something like that. :shrug: