Box 13 Retirement Flag Where only 12DD exists

We are trying to understand why the box 13 Retirement flag would be checked for employees with only Box 12DD (medical premiums) on their W-2 data for a particular company. These are non-working retirees who are provided health benefits.

We have confirmed we have nothing mapped to Box 13 field in the Tax Forms Definition page (although value 13 exists on the page, no taxes, earnings, or deductions are mapped). Box 12DD contains only medical deductions in the W-2 mapping; no retirement programs. We have also confirmed the Update Year End Reporting Info does not contain any deductions that would be considered medical or that are mapped to the 12DD box.