As encoding can go wrong on so many levels: I'm assuming that either the upgraded database or the app server or operating system or webserver is configured differently from the one you had before - with regards to encoding. And I might have missed one or two layers here.
Start looking at the components that you've changed - e.g. if you're still running on exactly the same database and schema that you've had on 6.1, the encoding probably didn't change. If you moved to a different schema, make sure that it's configured as UTF-8. Go up the stack from there (or start with the components that you're most comfortable with). There is no correct order to check and no component that sticks out IMHO.
