After a few years the character of Matilda was dropped and Walter was made less flamboyant.
Keep Circulating the Tapes: The first adaptation of Dennis the Menace was a puppet series shown on an early cable television station called The Children's Channel during 1990 and 1991. Virtually nothing about the show has been documented online, and the show's existence is rarely acknowledged by DC Thomson. It doesn't even get a mention in the 70th Anniversary book, History of the Beano or Ray Moore's Beano Diaries.
Justified in the case of Beano Diaries, as it was published in 1989.
The Beano have recently acknowledged the 1990/1991 series' existence here and here.
Missing Episode: CBBC skipped episode 26 of the 2013 series for unknown reasons.
It starts on July 8th 2013, but as with the comics, Mum and Dad have been redesigned. The cast has changed as well, with Dennis having a new voice actor. Basically, it's not a second season after all, but rather, a reboot.
Cowboy BeBop at His Computer: It's often assumed by the media that Dennis is no longer whacked with a slipper at the end of each strip because it wasn't politically correct. In truth, the practice of slippering had already become old hat by the time it was axed in the comic, and getting rid of it allowed for less predictable endings.