Interesting question, I use a P-2400 IT, but have never made any attempt at comparing it's output to input. I would have assumed that an isolation transformer effectively removes any relationship between the AC input hot/neutral and the transformer output. I guess one could measure the AC phase of the output and match it to the input, but that would seem to be an arbitrary relationship anyway.
..and I'd actually expect that most simply line testers would at least show some kind of neutral/earth fault when measuring balanced AC output.
..and I'd actually expect that most simply line testers would at least show some kind of neutral/earth fault when measuring balanced AC output.