In Samorost, each level exists as a different movie file. When switching to the next level, the background and music are meant to change. However, in Ruffle, the previous background and music track overlap with the next one.
Each level works properly if loaded independently.

Video: https://streamable.com/l4b2jz
Video (rybar.swf, by itself): https://streamable.com/u3yd8p
Game file: https://amanita-design.net/samorost-1/