I hardy believe this is true.
It is in the case of (at least some) people who created their My.Com accounts at the point of migration.
New My.Com accounts created through this site have not replicated to the primary My.Com domain.
The data is off Gpotato, but is not yet usable within My.Com.
The symptoms are having followed the Merge link from Gpotato, but being unable to log into the site once logged out, or unable to log into the launcher.
At the risk of my own account, I've created a new My.Com account, deliberately conflicting with my existing email address, and if I now try to change my username, it says the email address is in use, despite not being a changeable datum.