Not sure if its correct but my 2014 Expanda does the same. If the van is plugged into the car, my van lights are live even with my car keys in my pocket, and the van battery off.
When we free camp I pull the plug, to be sure I aren't drawing on the car
The switch in my 2009 Expanda only isolated the vans battery, and not any power coming from the car ... not sure how the new one works with the Drifter etc ... much more complicated than the other one.
Jayco have put the guy that designed it all (the only one who knows what, why, how) in a bullet proof glass case where no-one can talk to him, or ask him any questions. He's like the Kin Jong Un of the caravan land ... no-one dare approach him.
(He's next to the other glass cases with the plumbing dude, TV antenna dude, and theres a few other unlabelled cases as well, just in case you ask a different tricky question)