Ok, thank you. Excellent information in the reply. I can't work out what setting we previously had to made us avoid seeing this screen in the previous version, but it doesn't appear for anyone, and yet we still get a grade set. Something odd, I'm sure.
If the "congratulations" page were able to be formatted using the standard moodle text entry tool (and fall back on the current wording), rather than having to hack about in the language pack settings, then I think it would solve a number of peoples issues with this page.