2005 Mercury Montego Power steering pump

I recently had the power steering pump replaced on my montego, I discovered that after turning on the heater I was loosing power steering fluid.I took it back to my mechanic who stated that the pump was bad, so he replaced it with a new one. Well when you see fluid seeming to"bubble"from heat in the container, you panic, now I was told that it was from the bad pump, but when the pump was replaced I saw this again, my question is, is this supposed to happen?Is the power steering fluid supposed to boil or appear to bubble when the car is running?I hope you understand what I mean. Even when the heat is off, the fluid is still moving around in there, swirling, bubbling and what not.