I see
The new red and green ones had the old type regulators, but I still isolated the metal box with the pad and bush.
I think that might be a earth issue.
The way it works is that the cabin (chip) temp is output when the input wire from the thermocouple probe is shorted to earth.
When the button is pressed that's what happens. So any voltage supplied by the thermocouple then is also earthed.
But in the case of it rising a bit when there is a higher voltage input, ie, flooring it, I assume that there is a small amount of voltage not quite being earthed and that shows as that 3°C rise.
I think the (static) lower temp, 22°C, will be the chips temperature.
I testing I'm not sure now if I tried suddenly raising to 100°C and then dropping to room temp with the button was pressed. Just to something lower, and the temp remained stable.