Portal settings have been set to Sign Up all new users under a specified Enrollment Key/Department and with Username set to match Email address. If the "Users must be logged in to access shopping cart" flag in the eCommerce settings is unchecked, any new user who adds a course from the Public Dashboard, and creates their account during the purchase process, is given different fields and is able to choose a Username that does not fit the requirements set in the Portal Settings. These users are also not showing up on any User report and are unable to access their newly created accounts, but that's hopefully just a bug and tech support has been made aware.
