Missing Author dropdown in Post Editing

I’ve discovered in which case author dropdown miss! As said, I’ve two WordPress installation and I’ve shared users registration and login with this method: http://wordpress.org/support/topic/199522?replies=5 or http://www.davidbilbo.com/2009/05/using-a-single-user-database-for-multiple-blogs/.

With this procedure, author dropdown is missing in the secondary WP installation when I insert these lines in wp-config.php:

define(‘CUSTOM_CAPABILITIES_PREFIX’, ‘wp1_’);
define(‘CUSTOM_USER_TABLE’, ‘wp1_users’);
define(‘CUSTOM_USER_META_TABLE’, ‘wp1_usermeta’);

If I delete these 3 lines from wp-config.php of secondary installation, author dropdown reappear (but obviously).

Any ideas?