There is an issue with the relationship between users and posts (actually i noticed it on a custom_post)
when i connect more than 10 different users to a post, the others have their select box displayed in the metabox but no name inside.. and when i re-select a user and save the post, the select is still empty.
The query that retrieves the users to display in the combo box looks like this :
AND wp_users.ID IN (2,3,4,36,37,38,39,40,41,42,43,44,45)
ORDER BY display_name ASC LIMIT 0, 10
It looks like wp added an unexcpected limit to you original "include" query...
by just adding : $args['number'] = count( $meta );
on line 120 of the file /meta-box/inc/fields/user.php , i could solve the issue,
but could you give me a way to solve it from outside the plugin source ?