I recently posted a question about cutting the ground wire in an isolation transformer to make it truly isolated. After reading the responses, I decided the best advice was to reconnect the ground wire and just use a three prong to two prong adapter between the isolation transformer and the DUT. After I reconnected the ground I checked and confirmed that I had ground wire continuity from the wall outlet to the transformer outlet. Then, just out of curiosity, I plugged in one of those outlet testers from Home Depot (the ones with the three lighted indicators that tell you if the outlet is wire correctly). I expected that it would say that I had an "Open Neutral" since there is no connection between primary and secondary coils, but what it said was that I had "Open Ground". I checked the tester in a house outlet and it is functioning fine.
Is there some physics about transformers that would confuse this tester or is it telling me that even though I think I have good continuity through the ground wire, it isn't good enough?