I repaired a light fixture on 4-way circuit. When I went to put the fixture back up, I checked the wires with a Fluke volt tic. The tic lights up so I flip a switch and try again. Still light. Huh? So I try a Wiggy. Nothing. Ok, some kind of phantom voltage. As I'm hanging the fixture I brush against the hot wire and get a little zap.
The only thing different here is that the switches are lighted. Do they let some current through?