Horton Hears A Who

The Blue Sky Studios animated movie adaptation of Horton Hears a Who! has all the characters break into ''Can't Fight This Feeling'' at the end. According to the DVD Commentary, this was because they wanted to avoid a Bittersweet Ending where Horton has to leave Whoville behind and never talk to the mayor again, and that's all they could think of.

Example of:
Sudden Musical Ending