[DanCooper]

Default language for new tv shows is set by the language you've set for the source. You can check or change it also if you use Kontext Menu => Change Language.

What's the ordering of the scrapers? IMDB -> TMDB -> TVDB?

Thanks - language is set to English (eng-US) for this show.
Scraper order is IMDB -> TMDB -> TVDB, although I've tried disabling them and only using one at time, with no success.

All shows I've added to Ember since having this problem with Party Down are working fine, so it is a real puzzle!

It works for me in your ordering. Do you've tried to "change" to tv show (Context Menu => Change TV Show) to perform a complete rescrape?

FYI: For tv shows it's not really a good idea to enable all scrapers. Sometimes IMDB, TMDB and TVDB has different episode sortings or division (e.g. SpongeBob SquarePants).