How does a demotion affect an employee’s vacation accrual?

Q. "We are demoting a supervising attorney to staff attorney. Our supervisors have a higher cap on the amount of vacation time they can accrue before they stop accruing than the staff attorneys. After the demotion, do we have to allow the demoted employee to cash out his vacation time above the cap or does he lose it as part of the demotion?"  -- C., Calif.,