During flight, the radio window shows FIS/Tower/nearby airfield frequencies in different colors. While approaching my destination or alternate airfield I get not information about the frequencies I have to dial in - is this intentional ?

-mike@edtg

Yes, the feature is designed to operate only on your current position (and what you're doing) and I don't think it takes your plan into consideration at all. Certainly if you're nearing your destination you should see its frequencies, though, as by then it would be near enough.