Chassis and Coach cutoff switches don't kill the big inverters as they require far too much power to be looping them around the coach through switches, they are cabled directly to the battery. The house cutoff contactor kills only the coach. You didn't mention what remote and/or additional widgets you have on the Magnum, but the ME-RC and ARC panels are powered via the remote cable from the inverter. Unless you have the remote off module installed on the Magnum buss, the inverter will stay on regardless of having the coach powered or not. I have an optional buss widget that shuts off the inverter when I kill the coach batteries, but the inverter only goes into standby and cannot be powered On. Any of these big inverters can kill the batteries over time. I have a manual master house battery shutdown for emergency shutdown, but this isn't the norm.