I think the logic is to use the cheapest way of building the house without burning it down and maintaining code. I had to trace out that circuit with a tone generator. The one I mention also go to back facing security lights, and I was having the GFCI outlet in the garage pop taking out the lights, bathroom, garage etc. Annoying. I opened up every box and found a host of issues. Outlet screws not turned in just barely hitting the metal, grounded, moisture proof outlet boxes; they all were using the weak push in blade connection vs screws. You probably have some leakage on that line somewhere; doesn't take much, something like 5 ma differential between the lines. Does it happen after a windy rain? Check exterior outlets and lights.