Yes.
Unfortunately, Community Builder doesn't let us save a user if there's a field that's marked as required that isn't filled in. We're always working on ways to improve this, but until then, there's 2 options that will hopefully get you over this hurdle:
* If you're using the "Full Joomla Registration" setting (subject says you are), you can enable the "Show Required Fields At Registration" box in the CB plugin. This will show all non-mapped, but required, fields at registration for the user. Right now, if they leave it blank, it can still cause issues, and that's a bug we plan to fix soon.
* Mark that box as non-required.
Hope this helps, and sorry for the troubles!