Yes it is some what common. My jeep had the same symptoms a few weeks back. I flushed the heater core and the cooling system. The heater core i flushed one way and then the other, to get it flowing nice and free. I then re filled the jeep with some 50/50 anti-freeze (about 2 gallons) and we were blowing hot air again, and fast!
note: the coolant i flushed out was like pee soup, real dark green, with some streaks of brown (rust).