Unfortunately, it's not a bug in the slightest. This was because we didn't have a platform tool back then (before Snowy Escape) and the only was to achieve split leveling was to fake it. Planet Honey Pop in San Myshuno, Pan Europe in Windenburg, every stage of actor/actress career in Del Sol Valley... It's working as the game design indended.
The thing is, parts of these buildings are not actually rooms - they're walls on a foundation with no real floor. In case of Planet Honey Pop, the stage for the karaoke station is the real part of the room but the lower parts of the floor are just tiles places acroos the grass. As far as the game is concerned, it works like this: there's no real floor -> it's not a room -> it's outside space -> snow should be there.
If anything, fixing the lots to have platforms would be ideal. It can be done so we get new lots after creating new saves, just like there's refreshed townies like Goths etc. I only hope they get back to ALL "broken" lots like this, not only Planet Honey Pop. There's so many places that have this fake split leveling and should be fixed :}
