Korean Air Skypass - Award ticket booking

I have a friend who recently used his Skypass mileage for a reward booking. At first, he booked one-way without ticketing. Several days later, he added the return trip in the same reservation. The thing is that the COS of two legs is different. When he wants to issue the ticket, he was told that the whole trip was considered TWO one-way ticket not the ONE roundtrip ticket and he needs to pay more on the tax.

I am not sure if the KE agent got it right or not. Should my friend ask KE to consider it a ONE roundtrip?

I did it once in 2003. KE issued two one way tickets..

I believe If inbound/outbound class is different or inbound/outbound season is different (peak non-peak), you can not have one RT ticket.

I do not think tax differntial is huge. How much is the difference?

As far as I can see in the award booking, they consider it TWO one-way. So it is normal, isn't it?

The difference is $80.