garbunk on "Chinese characters displaying as question marks with utf-8 enabled"

I have a completely stock installation of the latest version of Wordpress. I wrote my first post in simplified Chinese and as soon as it was saved, it turned into question marks. The usual solution found on Google is to change your wp_config.php file to contain

define('DB_CHARSET', 'utf8');
define('DB_COLLATE', '');

However, this is 3.5.2 and utf8 is the default. Indeed, my config file already looks exactly like this. Yet I still get question marks. What could be the problem?