That's the way they all usually operate. Start off expensive, then price lowers in the months leading up to the flight if there is still enough capacity. Then, as the flight sells out, or getting close to the date, they go up.
This maximises their revenue per seat. Early bookers will pay that bit more to have peace of mind their ideal flight times/destination are booked. Later on, the bargain hunters hit the scene and discriminate more on price than route/timing. Closer to the time, people who must get whatever flight (business travellers on expenses, people travelling for family emergencies, etc.) book convenient flitghts with much less regard for price.