The studio DOES consider these six films (Saludos Amigos, The Three Caballeros, Make Mine Music, Fun & Fancy Free, Melody Time, and The Adventures of Ichabod & Mr. Toad) to be part of their official canon of animated features, just so there is no misunderstanding. But this has been a recurring subject among some Disney fans for several good reasons.
1) Due to World War II, Disney lost money from the premieres of Pinocchio, Fantasia, and Bambi, films that were so expensive that the studio had to put the lot of their upcoming movies on hold. When the US entered the war, Disney's resources turned primarily to military-commissioned propaganda shorts.
2) The package features largely utilized stories that were intended either as their own features, or as future segments for Fantasia. For the former example, The Legend of Happy Valley was condensed to be the second half of Fun & Fancy Free, which later became known as Mickey and the Beanstalk when presented separately. In the latter, the Clair de Lune segment for Make Mine Music was an already-completed segment intended for the first Fantasia. It was re-scored instead as Blue Bayou.
3) The tone of these features leaned towards the pop culture scene of the 1940s. The musical segments from Make Mine Music and Melody Time were more contemporary, and the stories in Fun & Fancy Free and Ichabod & Mr. Toad were narrated by some of the biggest celebrities at the time. Disney still occasionally does contemporary stories once in a while (Wreck-it Ralph, anyone?
), but I guess depending on how it's approached, it can age the films quite easily.
4) Even at the time they were being made, the piecemeal approach to these films were unpopular choices. They performed moderately well with audiences, enough to keep the studio from going bankrupt. But many of Walt's animators lamented how they were "stringing shorts together", and movie critics were mostly uninterested, waiting for the studio's next full-length feature.
This, more than the other three reasons, was why the package features had a "third-tier" status among Disney features. Almost never theatrically re-released, largely shown as individual segments, and among the first of Disney's animated features to premiere on TV and video.
I would like to discuss the films by themselves, but first, let's hear some thoughts from you.