Tove Jansson's Moomin books have been the subject of a number of anime adaptations.
Now, I'm not entirely sure on the dates of broadcast on the earlier adaptations. Or which episodes upset Jansson over the somewhat loose adaptation. Which is to say the presence of guns, booze and swearing.
ANN has the first season running 1969-1970, the second in 1972. Clive Banks states that the series started in 1972, and the first 26 episodes were the ones which took a liberty with the plot. Now ANN, mentions that the first 26 episode of the 1969 series had a different director to the rest of the early series (which were by Rintaro). However Bank's episode guide does list the 1969 series, and the titles of the first 26 episodes don't seem to match to what I know of the Moomin stories.
Therefore I'd be inclined to think that the Masaaki Osumi directed episodes of the '69 series are the suspect episodes. Especially when you consider Osumi's other credits include the original Lupin III series.
Anyway, there was a third series in the 1990s that the BBC broadcast. There a sequel series and a movie in addition to the first 1990 series. This series pulled stories and characters from the books, the Moomin comics (some characters like Stinky appear only in the comics) and some anime originals (the witch characters I believe are originals for the cartoon). The primary director was Hiroshi Saito, who had experience on various World Masterpiece Theatre shows (including the aformentioned Rascal & Perrine) – as well as directing other European co-productions like Alfred J Kwak and Vicky The Viking.
Now I couldn't find a OP clip in either English or Japanese. What I did find was this:
Clearly from one of the older series, from the look of it I'd say it's from the part of the series with Rintaro's direction. Whether it's the Mushi Productions part of the 1969 Moomin or from New Moomin, I don't know. It's some damn fine directing though.
Also… Anime News Network has the first series listed as World Masterpiece Theatre. It's not. It's not made by Nippon Animation, so it's not.