Outlets switch polarity when 3 way light switch is used

Man thank you for that q, as it's not everyday...

Clearly there's a wiring error of some sort; but not sure what you mean by 'polarity'

Can I conclude from that there's another switch, on the second floor, that also controls the third-floor lights

I presume you mean the ceiling lights of the third floor; suggesting that they're on a different circuit than other lights on the third floor, adding another level of complexity to your problem

Spider, no offense, as a former Jorn major I realize how difficult such expls ccn be; but after the better part of a century in the Electronics Biz I can't be of much more help; not that I've been of much so far

Sorry, polarity is the wrong word. What happens is that when I turn the third floor 3 way light switch on (either from the second or third floor) the receptacle test correctly (hot and neutral are on the proper prongs). When I turn the light switch off the hot and neutral switch prongs. I hope this explains it better. I have pictures of each situation but it doesn't look like I can post them on this forum.

Man, after some 18 years hereabout I dunno any easy way how to post photo either

Like I said earlier, obviously there's a wiring error but I will leave it to others who think deeper'n me

According to your profile you've been since 2012. In my book that is only 5.5 yrs. Furthermore, this A2K website was in its infancy 15 yrs ago. However, before that it was called Abuzz. Are you saying you've been a member when the site was aligned with the Boston Globe and called Abuzz?

Perhaps ...this is a guess and subject to wild inaccuracy ... you're linking your online activity within forums as part of one personal experience?

Rag it seems more like musta been 2000

At 86 w/ Alzie's, don't 'mem' much

Man, that could well be. Thank you for your interest in my plight