different tags in different language sites, why?

A Finnish member wrote in Finnish Librarythingers group about a curious matter. It must be a bug, because I don't see any sense in it. Tags on work pages (and maybe elsewhere, too) are different in different language sites. It seems that what is shown is dependent on which language site they are added.

Here are some examples:

Finnish site:
That was the week that was. No tags.

Same work in English site, tags: Humour(1) owned(1) Radio & TV(1) television

Finnish site:
Internet at Sverige. No tags.

Same work in Swedish site, tags: computers(1) internet(4) non-fiction(1) sab:p(1) SAB:Pucb

Finnish site:
Pussikaljaromaani. Tags: 2000-luku(1) 2004(1) 2007(1) 2009 luettu(1) alkoholismi(1) beer(1) contemporary(1) debut(1) drinking(1) Eendagsroman(1) favourite(1) fiction(8) fiktio(2) finnish(5) finnish literature(1) hard cover(1) helsinki(3) Kallio(3) kaunokirjallisuus(1) kotimainen kaunokirjallisuus(1) Library(1) novel(1) oma kirjasto(1) one day novel(1) romaani(3) romaanit(1) rtw09(1) Suomi(2) top 100(1) where?(1) yhden päivän romaani

Same work in English site. Tags: 2000-luku(1) 2004(1) Eendagsroman(1) favorite(1) fiction(8) finland(1) finnish(3) finnish literature(2) finnish poetry(1) Kallio(2) oma kirjasto(1) on loan(1) poetry(1) romaani(2) top 100(1) where?(1) Yhden päivän romaani

Swedish site: no tags.