The old Confluence LDAP connector supports multi-valued fields.
The new LDAP connector does not and Confluence shoud regain that feature, as it helped really much in an organization where multiple userdirectores get combined into one big directory.
Here is an example of the LDAP fields where a user would have three different logins which all refer to the same identity:
Groupmembership is searched via CN. Confluence searched the Loginnames field for checking the credentials and getting the comlpete DN for groupsearches (for instance: cn=E01010101,ou=users,dc=domain,dc=com).
Confluence 3.2.1 works very well with this setup, looking up the correct user information by CN.
Confluence 3.5.13 only finds user "Domain_B.USERNAME".