St Kilda-Brockville-Halfway Bush is a commercial route operated by Citibus and they don't have to follow any rules of the Otago Regional Council. This is why they sometimes run quite old non-accessible buses, and have slightly different fares.
At night and on Saturdays and Sundays and public holidays, as the passenger numbers drop off, there's much less money to be made from selling tickets so the bus route becomes an Otago Regional Council-subsidised route. The ORC contracts to whoever is cheapest, so at the moment Citibus doesn't run the service on nights, weekends and holidays, Passenger Transport runs it, and as an ORC contractor, they have to use ORC-approved buses and ORC standard fares. This confuses a lot of people.