I did a re-inspection on a home today. The ungrounded receptacles in the kitchen had been replaced with GFCIs. When I tested one of the receptacles with a plug in tester, the tester did not light up at all (the tester worked before and after testing this receptacle). When I pushed the test button, it tripped and when I pushed the reset button it reset. I used my non-contact tester and it lit up as soon as I got it near the receptacle indicating that there was power to the receptacle.
I have never seen a GFCI trip and reset without power so unless there is something new, the receptacle did indeed have power.
The tester worked before and after testing this receptacle. The 3 light tester is OK. I also didn’t pull the receptacle out of the box to do any testing on the wiring. I tested for power with a non-contact tester and it indicated that power was present as soon as it got near the receptacle.
I was asking for my own knowledge as I have not encountered this before. I could understand the problem being a disconnected neutral, but then I do not think the GFCI would reset.
I carry a multimeter but very rarely use it. The only time recently that I used it was when my 3 light tester showed an open neutral. I thought the tester had a problem so I used the multimeter and, sure enough, the neutral was open. I then went to another room and found a light fixture with a 2 prong cord and showed the buyer that it would not work in the receptacle even though it had power.
I will normally not pull receptacles out of the wall (my own home, yes. on an inspection, no). I am not an electrician and if anything were to happen, even if not related, I would not be able to explain why I was taking apart an electrical receptacle. This was just a weird happening that I could not answer so I wanted to find if anyone had an explanation.