GateIn is configured to use LDAP (OpenDS 2.2)

when I try to create two users with usernames:
1. viliam
2. viLiam

only the 1st one is created. after trying to save the 2nd one, I've got error with message "Unknown error" while in server.log there is:
Caused by: javax.naming.NameAlreadyBoundException: [LDAP: error code 68 - The entry uid=viLiam,ou=People,o=portal,o=gatein,dc=example,dc=com cannot be added because an entry with that name already exists]; remaining name 'uid=viLiam'

I think that the error message should be more specific (the error is known).