LDAP provider is setup
User/Password provider (created) but disabled.
LDAP provider does NOT allow registration, i.e. an admin needs to import the user.
The user try to login before the admin does anything, and fails.
The admin try to add the user using the "Import from LDAP" screen
The following error comes up:

Failed to add USERNAME
#1062: Duplicate entry 'ldap-self-USERNAME' for key 'account_details'

Even though an error message is displayed the user is added to list of users.
The user CANNOT login!!!

The only way I found to solve this was to remove the user using the "Delete User" screen and then manually delete the table record for that user from user_externalaccount