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.