LDAP Users duplicate on the LDAP group after each authentification

My LDAP is setting with "LDAP Admin Application" extension.
I use LDAP groups mapping.

When a user is connecting, the login is added automatically in the group (normal).
But when the same user connecting again, it's adding the login (Username) in the group one more time (see attachment).
Is it normal ?

Comment:
If I try no add the Username manually in the group, it's impossible if the Username is already in the group.