Author Existence Failure: According to some members of the show (see below), the show was cut short due to Mel Blanc's failing health. Curiously Blanc still performed several voices after the series up until his death however.
Keep Circulating the Tapes: Various DVD compilations were released in the mid-2000s which are now out of print. Shout! Factory released the first 24 episodes before losing the rights to the series. Mill Creek Entertainment released the entire first season on DVD, one half in 2012 and the other half in 2013. Finally averted in August 2016 when Mill Creek released the entire series on DVD, including the previously unreleased second season episodes.
Off-Model: Sometimes, Wordsworth's skates would disappear from his feet in between shots; it's especially noticeable at the start of the episode "Junk Food". In Season 2, Hector's ears would sometimes be colored beige (they're normally black), and then there's Cleo where sometimes her entire being was drawn horribly, such as in the episode "Hector's Takeover".
Screwed by the Lawyers: Ever wonder why Heathcliff and Riff-Raff never meet outside the end credits? Heathcliff's owners at the time, the McNaught Syndicate, apparently didn't want characters not created by them appearing with Heathcliff, so hence Riff-Raff and Cleo were both unable to appear; Hector, Wordsworth, and Mungo were created specifically so they could appear in both segments.
Talking to Himself: Riff Raff and Wordsworth were both voiced by Stan Jones, and then there's Mungo and Leroy, both voiced by Ted Ziegler.
Urban Legend of Zelda: Often times, someone will claim, or swear they saw an episode where Heathcliff and Riff Raff actually meet, but the episode only aired once for whatever reason. No such episode was ever made; the only time the two characters interacted was during the end credits and an odd cameo from Riff Raff in the comic strip.