I was always planning on using a ZW dedicated to powering the switches and all the accessories; seperate from the other ZWs (I was however, planning to phase all ZW's and connect them together via the Common terminals......should Inot do that and keep the accessory ZW completely seperate??).
But you've peaked my interest. If I understand what you're saying, DC current can "sneak in" to the center rail through the switches external power tap? Is that correct?