Adaption Displacement: Nobody knows that the 2003 cartoon was based on the 1988 animated short film of the same name, which in turnwas based on the short animated film The Peep Show from 1962, which is also extremely obscure.
Broken Base: For some fans, the final two seasons aren't considered the classics that the first three are. It doesn't help that season 4 came nearly three years after season 3, and in that time the TLC network it had been on since the beginning shut down, and KCTS began airing it with Pocoyo. The Vocal Evolution the main cast went through didn't help.
Screwed by the Network: Unsurprisingly, by RTM2 in Malaysia. The show wasn't given a consistent schedule, was frequently pre-empted for sporting events, and only one season was aired. It was later picked up by Discovery Kids Asia, except Discovery Kids Asia got screwed by its provider in Malaysia, who dropped the channel just three years after picking it up, with the excuse that it wasn't showing anything new or interesting...
Seasonal Rot: Season 4 for some fans—partly due to the fact that the first three seasons were classically a lot better. Season five seems to have improved these mistakes, however.