Hi,
You say that it is full of bugs.
We have released it more than one month ago and waited for feedbacks from users during all that time before pushing the update to everyone. In the mean time, we got lot of feedbacks from lot of users and fixed a lot of things and only pushed the update recently, since no more bugs were reported and had been tested extensively, both on our end, and by plenty of users. So it is incorrect to say that it has not been tested correctly.
There was no bug reported the state/country fields on that release and it's working for everyone else (thousands of users).
So it means that it must be something specific to the website.
The behavior you're describing happens when you removed/unpublished the country that was selected as default in the custom country field without saving again the custom country field with the new default value. So I would recommend to edit the country field via the menu Display>Custom fields, make sure that it has the default value you want and then save the custom field.
If that doesn't work, it might be coming from something else, like a javascript conflict with something else on your website (unfortunately, we cannot anticipate conflicts with the thousands of extensions out there) and we would need to see the checkout as well as your settings to be able to say more on the issue.