The fact that this series has some continuity with the Classic Disney Shorts can help explain all the characters' actions.
In the episode "Fire Escape", Mickey was quick to anger at Goofy for making those suspicious remarks about Minnie. Mickey was probably still sour about the time Goofy had made advances on Minnie in "Ye Olden Days".
In that same episode, Mickey's sheer panic around fire is likely due to his previous fire-related encounters where fire has shown to not only be sentient but also flat-out malicious.
Donald's Jerkass Ball in "Roughin It" could stem from his previous experiences trying to camp out in the wild.
Mickey and Goofy choosing not to tell Daisy about Donald's Jerkass behavior at the end of "Bronco Busted" is because they know Laser-Guided Karma will somehow find a way to screw Donald over and telling Daisy, who has made several cases of being a Jerkass herself to Donald, would lead to her immediately dumping him should he come back to her.
Here's the reason why these characters appear in "Keep on Rollin".
Yen Sid is enjoying Disco Night because his first appearance was in Fantasia, a movie that revolves around music.
Pete recruiting Ursula makes sense since she had once stolen music by robbing Aerial's beautiful voice.
When the Witch shows the children-turned-pies to Huey, Dewey is noticeably missing among them. It's heavily implied the pie Huey just ate was his brother.
