My Categories are all ‘???’ question marks

I can’t create or view categories which have Japanese characters in them.

When I first upgraded to 2.5, my entire blog was unreadable, which I fixed by adding the character set ‘utf8’ in my wp_config.php. Now all the posts and everything in the dashboard with japanese characters, shows fine.

Except “Categories”. All of my categories, which use japanese characters show nothing but question marks ‘???’

Even if I edit them and re-type the japanese characters, it still turns them back into question marks! Any way of stopping wordpress from creating question marks?