That said I'm a fan of jointly controlled "free states" in questionable ethnically mixed areas such as Northern Ireland, the Trieste/Istrian peninsula area, and of course Bosnia. Of course, most of Ireland should be Ireland and South Tyrol should have been kept with Austria.
South Tyrol was mostly Italian and Italy lost 600 thousand fighting for the allies. They couldn't send them away empty handed after that. Italians actually thought they were given too little territory. Of course this is incorrect, but not giving them at least the Italian part of South Tyrol would be an even greater injustice.
And Croats and Slovenes are South Slavic, not West Slavic.
http://en.wikipedia.org/wiki/Slavic_languages