[CRLS222]

I had a receptacle that popped and flashed for a moment, but didn't trip the breaker.
I checked the upper and lower for polarity, etc.. And both are correct. When I opened and looked at the receptacle, the two right screws had black wires, and the two left ones have white wires, with the ground wire screw connected on the left underneath the two white wires. I was going to change out the receptacle, and turned off the breakers for the room so there would be no current. However, even with no power, when one of the white wires is being unscrewed, it arcs and my indicator that sticks in the slots indicated a Hot/Ground Reverse. I don't understand.. I thought if the breaker was turned off and the receptacles are not on, that there wouldn't be a current. I don't know what to do.

[tkrussell]

Need to confirm if this circuit is sharing a neutral with another circuit.