When someone invite someone else, the user creates an account based on a link received by Tuleap, we can assume that the email is correct so it seems useless to ask for email confirmation.
In order to work, we should add a token in the invitation email and do not let people change their email when they create from this link.
All this is needed to ensure that the email is valid (so people can receive password reset email when their account is lost for instance).