Wireless sensor set to measuring device in a room with no zone controller still activates the zone

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I am intending to control a bathroom's ufh by replacing the original wired thermostat/timer (on the outside wall of the bathroom with a remote wired sensor inside the bathroom) with a TADO wired thermostat combined with a wireless TADO sensor inside the bathroom. I'm trying this out first by using the Kitchen TADO wired thermostat (that controls the UFH in that room) and setting a wireless TADO sensor to be the Kitchen Measuring Device. I can see that the wireless sensor is overriding the wired thermostat ok but it is also still activating the rest of the house's heating zone - even though the Kitchen has no Zone Controller assigned. How can I stop the wireless sensor activating the heating zone?

Thanks