I guess my question for OP is why bother cancelling out the Polaris upgrade part? IMHO Polaris is easily worth the $600 copay for such a long flight. I can't comment specifically on Premium Plus but suspect an arguement could be made that the difference between Premium Plus and Polaris is much greater than that of E+ and Premium Plus. Lie flat seats, Polaris lounge, decent meals and booze.
If the Polaris upgrade doesn't clear they should only charge you the Premium Plus cost which I believe is purely miles (correct me if I'm wrong here)
-James