Water Pump Question

This same thing started to happen to my RV this last summer. What I do is after turning the water pump off I open a faucet to relieve the water pressure in the system, then hook up the city water. This works,however this isn't the way it is supposed to work. As mentioned here there must be a valve that sticks open in the system and relieving the pressure let's it close.. I have in the past,when I first got the RV, made the mistake of hooking up the city water with the pump power on. I don't know if this did anything but there is a sticker near the switch that warns against doing this. This is our first RV and missed this step in the excitement of setting up.