This is quite odd. If I wanted to go from Boston South Station to St Albans, VT, it will not show me any connecting itineraries. It will error out saying that there is no service for what I am looking for (BOS-SAB). However, if I try to search it as a multi-city, it will let me book the BOS-NHV or BOS-SPG and the NHV/SPG-SAB separately, and will price both legs separately. This behavior exists in both the site and the app (although the app doesn't give me the option for multi-city ticketing)