I was reading the Lightwave instructions, and it says So if there is no wired connection, why work it matter where the switch gets power from?.
The Live still needs to be on the same circuit as the Switches outputs though.
Indeed you can likely reconfigure connections for it to work on TWO circuits, simply by feeding the UPSTAIRS switch from the UPSTAIRS circuit and the DOWNSTAIRS switch from the DOWNSTAIRS circuit.
Indeed Flameport explained this but i feel its out of the OPs grasp.
But if I read correct this switch appears to be on 3 circuits somehow