Thanks, but that does not address my question.
For federal taxes, you might still be subject to the underpayment penalty if you did not meet the proper conditions on each of the due dates for estimated tax payments ("quarterly"). For example, if you make no tax payments during the year, but pay more than 100% of your total tax liability in December, resulting in a refund, you are likely subject to an underpayment penalty -- unless all of your income were in the last quarter, or you made that more-than-100% tax payment by withholding from earned income, ya-da-ya-da-ya-da. But according to Calif income tax instructions, it would appear that is not the case. The instructions clearly state that if the "tax due" line is zero: "Stop. You are not subject to an estimated payment penalty". I now know that those instructions are wrong! Even though I got a refund, I got a notice from the FTB stating that the refund was reduced by an underpayment penalty (amount stated). (And no, I did not make just one tax payment in December. That was just an extreme hypothetical to make the point.)