ABC Code Maintenance - 8.03.403D

I have been trying to set-up ABC codes using the minimum unit cost and
can't get it to work. All of the items end-up coded with the lowest
code, in my case "C" regardless of the unit cost. I've checked the
obvious - cost method, units costs, etc. The minimum dollar volume
works fine. Anyone out there using minimum unit cost in this version?
If so, any trouble or hints?