Is it just me or that there seems to be problem booking Comfort Class RT online to Asia if you want to stay at IST for 2 nights?

For example, I tried booking JFK-IST-HKG (or NRT) RT, it works perfectly. However, if I want to stay in IST and make a multi-city booking, for some reasons, all segments become Economy. In reality, the only difference is IST-HKG segment leaves 2 days later. Is there a fix/way to get around this online or I need to call reservation line? If this can only be done over the phone, will the fares be a lot higher? Currently they (Comfort RT) range between $1500 to $2200 if you don't travel during peak period.