Right. What you are seeing is not a bug, rather the fact that Chrome has actually implemented the internationalization API, which this script makes use of when available. This makes it possible to get a more precise timezone than in other browsers.
The purpose of the script, however, is not to provide the most precise timezone applicable - but to find A timezone that correctly describes your system timezone. So this is expected behaviour. Since Tokyo = Seoul in modern times this script has accomplished its mission.