Have an old house with knob and tube wiring that has had newer wiring added over the years, hard telling what's behind those walls. Have some gfci's that show reverse polarity. The wiring seems correct(black is showing it is hot and on the correct side of gfci). Switched wires, same results. Even put new gfci in. I am stumped. Anyone ever had a similar situation. House is to be inspected and needs to have this fixed.