I'm sure you have the idea by now, just thought i would give you another horror story. I used a circuit tester when moving wiring in a wall. It read hot, I assumed it was a full 110 volt. continued with my wiring, sealed up the wall pugged refrig. in,,, no worky. tested outlet w/ multimeter 6.4 volts. enough to light "hot stik" NOT enough to light refrig. Had to rewire entire kitchen after I had finished walls(wife not happy).Upon inspection found original electrican had "back fed" some of the house. Sounds like you are in a similar situation.