I encountered a problem with 3.0.4RC1, specifically with the get_username_string() function.

When you do not include the fourth parameter of get_username_string and you have more anonymous posters as last posters, the first one's is used for the other poster's.

Data are stored correctly, the row for the forum has the correct last anonymous poster, but another is shown instead. It is only a data display problem.

This fixed the bug, functions_display.php, add fourth parameter $row['forum_last_poster_name']:

'LAST_POSTER_FULL'        => get_username_string('full', $row['forum_last_poster_id'], $row['forum_last_poster_name'], $row['forum_last_poster_colour']),  

Now the $cache_key in get_username_string is unique and the names are shown correctly.

Replacing the get_username_string function with the one from 3.0.3 also fixes the problem.