Just configuring a new DNN site where we want users to use their email to log-on but we also want to allow them to logon with SocialNetowrks

The problem occurs if a user opens to accounts, first by email, then by SocialNetwork, but this works


But as soon as an admin try to change anything on /Admin/Site-Settings an error raise :
"There are duplicated emails in the actual list of users, If you want to use the email as user name first must verify emails are unique"
(not exact sentence, my DNN is in spanish so)

I understand the "warning", but it should allow me to continue as usernames are uniques (email@email.com & Facebook-email@email.com are different)

How we should configure DNN to allow this ?

On the other hand, we want to offer the possibility (not the obligation) to allow a user to log on with different systems and "merge" the accounts, so we should allow him to have different means of logon with "same email" ...