Named Selection Sets changing to random selections

[Anonymous]

Hi all, quite new to 3DS Max and enjoying it so far but this is really frustrating me. I'm creating selection sets, but when I try to recall them they just come back as randomly selected polygons. This happened earlier today and I lost about 2 hours work. I started again and checked as I made them to see they were recalling correctly and all was fine. Saved it, closed it, came back and it's doing it again. Another 2 hours work gone.

As an example, here's the selection set I created as "windscreen". When I called it back during the same session it was fine

Then I've gone away and come back, and when I've tried to recall it again it's come back like this:

Same goes for the dozen or so other selection sets, all random, no pattern, all over the place. Am I saving them wrong? Is this some sort of error? It's absolutely infuriating!

Using 2017, Windows 10 (latest update).

[RGhost77]

After make selection set are you add new polygons to object? Selection Sets stores index number of polygons. When you add a new polygon order of polygons can be changed but not in Selection Set.

So Selection Sets works good only in you don't add new polygons/vertexes/edges.