They are day use moorings only not intended for overnight use. I doubt the mooring shifted since the are on screwpins into the bottom. They can only fail not drag. More than likely you got backwinded or a current shift. With a normal wind the one ball will be almost at the stern of a boat on the Eastern ball if no boat is on it. The anchorage there is not protected enough for overnight use regardless of the type mooring.
G