Thing is I don't trust the tester I'm using ...
Indeed - and, as I've said, I'm not sure that any of us do - or, rather, that any of us are are sure what it is doing and what its reported results mean, even if it is 'working as intended' (which it may not be). ... and you seem to be in the same position, given the "may", "possibly" (x2) and "might" (and your last sentence) when you write:
The PAT tester does an Earth continuity test and gives the resistance with a pass or fail, then it does an IR test and gives the results including a pass or fail, then for extension leads it does a polarity check - it may also be doing a resistance check - possibly along each individual wire (end to end) and comparing them and shorting the ends out (I think I hear a relay click) and doing a full loop (possibly) however when it has finished it either gives it a pass or if it fails it might (just might) give a vague reason why.
You go on to write:
Short - indicates a short between the connections - does not say which (although logic suggests its L>N as otherwise it would fail the IR).
Open - indicates the L>N are open circuit
Given the above, how are you sure of that - is that stated in the manual? As SUNRAY has said "Short", or even "Short circuit test" has been known to be used to mean an L+N loop resistance/impedance test undertaken when the L&N were 'shorted together' at the other end!
That's why I fudged an IR test on the L>N which suggested its 0.2meg so its a high resistance short .... The thing that really puzzled me about these leads is that it says there is a short yet I cannot find it using other equipment, it does not say its a direct short, or a high impedance short - just "short" (not very helpful).
That's the crazy thing about what you are seeing/reporting - and the reason why I suggested early on that I 'suspected' your machine. To electricians, there is really no such thing as a "high impedance short" - a "short" is generally taken (often defined) as being 'of negligible impedance' (usually <1Ω, certainly less than a few kΩ). If the "short" test is looking at the L-N resistance/impedance, then it's doing the same as an L-N IR test - so it's impossible that that resistance can be high enough to pass the IR test yeat also low enough to be called "a short"!
And your partially right John, in that I'm not 100% in what I am doing or the results as AC theory was a long time ago for me and I have not had much dealings with it at this level since, so I have forgotten a lot of it, I'm more of a lower voltage electronic person. ... Would you be comfortable figuring out the impedance characteristics and keeping multiple set of differential pairs within their correct skew while routing a PCB with them on, going to an IC with over 2000+ connections on? I would! So "idiot" is a rather offensive term to be using in a reply.
You seem to have misunderstood. I certainly was not suggesting that you are an idiot, and am sorry if you got that impression. Indeed, the fact that you are querying this result, have investigated it logically (using other equipment) and are discussing it knowledgeably and sensibly indicates that you are anything but an idiot!
What I was doing was commenting, in general, on the mention of attempts to produce (what are colloquially described as) "idiot-proof" products ('hardware' or 'software') - designed to be theoretically usable by people who had no understanding of what they do, how they do it, what should be done (and why) and no real understanding of what the 'results' mean.
I'm sure that there are many things that I do professionally (in fields remote from anything electrical) that you wouldn't have a clue how to do, and equally sure that the converse will also be true - but that does not make either of us idiots. What I would not be 'comfortable' with would be for you to be given 'a box', or piece of software, which seemingly enabled you to do what I do without any knowledge or understanding (just 'an answer') and I'm sure you would feel similarly if I were given a box or software which seemingly allowed me to do your PCB design - again, with minimal understanding.
So, 'idiocy' does not really come into it (for either of us!). I would, however, personally say that it is 'unwise' (i.e. I would be uncomfortable to do it myself) to utilise (let alone 'rely on') a bit of hardware or software if I did not have a reasonable understanding of what it was doing, how it was doing it and what the 'results' actually meant.
We all know of the potential pitfalls of 'blindly' relying on 'black boxes' or machine logic. In the early days of computer, an oft-quoted hypothetical example was that of a piece of software designed to advise the user which of two watches they should buy - one that lost a second every day and the other that didn't work at all. Needless to say, the computer chose the latter. Someone who 'actually understood what it was doing' would/should have realised that what it was doing was calculating how often the time it indicated would be 'correct' - and that the "buy the one that doesn't work at all" result arose because that one would indicate the correct time twice every day, whereas the former would only be correct about once every 118 years! An understanding of what technology 'is actually doing' can be useful in such situations!
Kind Regards, John