I have a water model with multiple pressure zones. There is one main low pressure zone that is fed by reservoirs and a couple storage tanks and there are 4 other parasitic higher pressure zones that feed off the low pressure zone. 3 of the 4 pressure zones have their own storage tanks. The 4th pressure zone has just a booster pump that kicks on and off depending on the system pressures seen at the station on the discharge side of the pump. This booster station feeds a couple dead end water mains that go up a steep hill. I am getting a "disconnected demand nodes detected; hydraulic results are likely to be compromised" error when the pump is off which isolates that zone from the low pressure zone which has the water sources. How is a situation like this modeled?
Usually when a pump to a dead end zone with no storage turns off, the customers are without water.
What may be happening in your system is that there could be a bypass check valve around the pump station that enables water to flow around the station at times when the pumps are off. This will result in lower pressures in that zone, but depending on the elevations, the customers will still have some water.