I have exactly the problem listed in this forum post:
I'm not able to create any Joomla user via a CiviCRM profile form, because the Joomla user registration fields do not appear on the profile.
- the "Allow User Registration" option in User Manager is set to "yes"
- I've tried setting profiles to both "Give option" and "Require" Joomla account creation
- I've tried custom and simple out-of-the-box profiles
- Permissions all seem to be correct (anonymous users are allowed to create profiles, see all custom data fields, etc.)
I do also have Community Builder installed, but as far as I could discover that shouldn't cause any problems with the fields appearing.
Any ideas what else to check, or how to troubleshoot this further?