These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Adaptation Displacement: There was a 1950's short, too. It's vaguely remembered, though it was put on the DVD release of the 1998 film.
In the books and early specials, Madeline's parents are known to be alive, and even appeared in the Christmas special. The live-action film, in which she's an orphan, caused DiC to retcon her into an orphan, much to the confusion of many.
All Animation Is Disney: DiC was with Disney at the time the series and Lost in Paris was created, which made many people believe that the Madeline TV series and first Direct-to-Video movie were from Disney (It doesn't help that Lost in Paris, at least the original 1999 release before it was rereleased on DVD by Shout! Factory, opens with the text "Disney Presents")
Ear Worm: "I'm Madeline", "A Bad, Bad Hat", "Two Straight Lines", "Something is Not Right", "Have You Seen Our Dog?", and every other song.
"Home Is Where The Heart Is".
Harsher in Hindsight: Lost in Paris, a story about a girl named Madeline being put in a sweatshop, becomes this after the 2007 abduction and possible murder of Madeleine McCann.
Hilarious in Hindsight: CINAR came up with the initial ideas for the specials and partnered with DiC to execute it. Then Cinar went their way when the partnership ended while DiC went on to make the the TV series and two specials. Almost two decades later, CINAR became Cookie Jar and subsequently bought DiC, and then merged.
Mary Sue: Madeline herself, especially in the early specials. Though she later pulled through, especially in the live-action film.
Narm: "Lord Cucuface, beware! Genevive, noblest dog in all of France, you shall have your ven-ge-ance!" For the record, that line did not appear in the TV special. The movie did include the second sentence, albeit with a normal pronunciation of "vengeance."
No Export for You: The specials. They have never been broadcasted in a few countries worldwide compared with the rest of the series, and even in terms of DVD releases they have only been available as digital downloads on US-only online stores.