Well, after fixing the two switch box two days ago, I finally got a chance to get back down into that outlet box to see if I still had stray volts. I turned of the single breaker that this outlet was wired two, and opened up the outlet. I disconnected everything with the box, and probed around, and saw zero volts everywhere. I also went back downstairs, and probed the wires going to the basement/outside light that this outlet was feeding. Everything was zero volts there also.
So, problem is resolved, and root cause confirmed. See thread above.