Fantasia

When he made Fantasia, Walt Disney originally thought of it as a concert feature (that was the original title) which would change over time. He planned on releasing the film once every now and then, replacing some segments  by new ones. His wish was partly fulfilled when the Disney studio made Fantasia 2000.
However, Fantasia hasn't waited 60 years to be altered over the years. First of all, a sequence planned for Claude Debussy's Clair de Lune was cut before release because the film was considered too long. It was later used with a completely different soundtrack in the film Make Mine Music in 1946. Here is the restored sequence with the intended music :

Also, the elaborate sound system called Fantasound used when it first came out was only used for a roadshow exhibition but when it went on general release through RKO, the sound was mixed to monaural to accommodate the more modest equipment of the majority of theaters throughout the world. Deems Taylor's live action scenes and the Toccata and Fugue segment was cut.

In 1969, the film was once more released and, for the occasion, four short scenes were also cut, this time for censorship purposes. In the Beethoven sequence, a black centaur helps a white one to prepare for the arrival of the male centaurs. The few shots were she appears were cut and the gap was filled by repeating other shots and flipping them so they wouldn't appear too similar. It is ironic to think that this black character, Sunflower, was featured quite prominently on the French poster of the film.

In 1982, in an effort to bring a new sound, a new recording of the score was conducted by Irwin Kostal and new vocal introductions were recorded, therefore replacing the entire soundtrack.

The first decent attempt to restore the film occurred in the early 1990s. The original negative was used as a basis for it and the original Stokowski recording was dug up, as well as some of the Deems Taylor segments. None of the shots of Sunflower were restored.
When the Bu-ray edition was released in 2010, further digital restoration was made and a few live action shots were added. However, since some of the audio portions of the Deems Taylor introductions were missing, it was decided that his voice would be dubbed by Corey Burton over the entire feature.

Also, Sunflower was once more missing, causing great controversy over the release among dedicated fans. However, thanks to the restoration technique used (each frame was scanned and cleaned up), it became easier to keep the shots were she appeared and erase her from the frame instead of cutting the shots altogether.
I personally regret that decision too. I was a child once and watched the Silly Symphony short "Three Orphan Kittens" repeatedly. I was surprised to see that short in the bonus sections of the Silly Symphonies DVD and had to actually watch it again to understand why there was any controversy. There is a black servant and a black doll in it and I suspect their design and purpose is considered politically incorrect nowadays. I do not think that I was influenced in any way by these images as a child and I consider myself a very tolerant person now. If needed, I thought the solution of having Leonard Maltin explaining beforehand why the film was kept intact was a much better decision than erasing the problem and pretending there never was one to begin with. Oh well...
 Here's the full sequence as you cannot see it anymore :

In spite of the changes, the Blu-ray is just stunning and I still very much recommend it.
That's all for today folks! Merry Christmas!