kitchen tap is open when you turn on the bathroom tap you start the pump running and this gives water to both taps. or a short in the wires when the bathroom tap is operated.
------------- the only silly question is the one you do not ask.
I looks as though the pump is being switched ok,but kitchen tap is not seating to shut off water and the flow is only stopping because the pump is switching off.Looks as though you will have to take tap apart to investigate.May need new tap if you cannot get parts.
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