Creator Killer: The small outbranch of Hanna-Barbera that was Turner Feature Animation (which had previously been H-B's own feature arm) had its' short life end here- it was folded into WB's own Feature Animation arm, which itself was eliminated by 2003 after their own string of flops, some of which (like The Iron Giant) became cult hits themselves.
Dawson Casting: Relatively averted. Darla's voice actress was about 12 when doing the movie (though Darla may have been a bit younger than that), and her singing voice was even younger.
Invisible Advertising: There was exactly one (we repeat, one) poster released for this movie. This might as well explain why the film was barely a blip on the radar when it came out, aside from that and a few Subway toys.
Don Knotts's (T.W. Turtle) brief singing role is filled by session singer Rick Logan.
For the singing role, Ashley Peldon (Darla Dimple) was replaced by Lindsay Ridgeway.
For Sawyer, the non-singing voice was provided by Jasmine Guy. Singing, Natalie Cole takes over.
The Other Marty: According to Lauren Faust, Jasmine Guy was a last-minute replacement for another actress, possibly Nancy Giles. She wasn't hired until all of Sawyer's animation had already been completed!
This would explain why Sawyer's speaking voice and singing voice sound radically different in the final film. Giles' voice would have been a better match for Natalie Cole.
Permanent Placeholder: The voice of Max the Butler in was provided by director Mark Dindal, though it wasn't supposed to be that way. However, because the production ran out of money later on, the producers decided to retain Dindal's scratch track for Max instead of using another actor.
The film was originally intended to star Michael Jackson, and would've incorporated a mix of live-action and CGI. However, Jackson dropped out, Turner acquired the script and the rest is Executive Meddling history.