vsftp user-names

Hi, I set up a vsftp (2.0.5) service on a RHEL5 und have the ftp users in a jail. But even if there is a etc/passwd in the jail root directory the user names don't show up with an ls command in a ftp session. Instead only user IDs are visible, like here: drwxrwx--x 2 51223 1145...