When I upgraded from 4.0.2 to 4.4.1, I received a message stating there were a few accounts that were duplicated between the parent portal and child portals and that 4.4.1. was handling user accounts differently now (allowing same logins between portals or something) and that the logins might be affected. 

Does anyone know specifically how user accounts between portals are being handled now?  I thought I read somewhere (but can't remember where now) that you can use the same login from parent to child now, but you had to create the login in the parent portal first.  I have a child portal with over 500 logins.  I am going to be creating some new child portals and users on the first one will need to be users on the new one.  Is there a way to have one large user base and just set permissions on portals from there? What is recommended in this case?