We are using "normal" uids for internal users (e. g. testuser) and email addresses in the uid field for customers with the new user management via LDAP. All users (regardless of the user type) can log in. But in the user management overview the users with email addresses do not appear. Instead of them internal user are shown up twice - in my opinion the last internal users that were read from the LDAP directory before an "email" user was read respectively.

Is this probably a problem with the "@" character in email addresses?