this is the room it opens into

I have a 1931 house with an unheated back hallway. I've never had a problem with paint coming off the walls. However, I do know about the problem you're describing - fastest way to strip paint off old woodwork is leave it out in an unheated space and the top levels of paint just fall off

I suspect it has to do with latex over oil issues since latex expands and contracts differently than oils and possibly some moisture problems also. Just curious...is the old underlying layer a gloss paint? In my back hallway, I painted latex directly on unpainted plaster walls and that is one difference I could see between the two spaces.

HI -- I would not do the mirror tiles in there . I think you should cover the walls with some of that wall paper that will hold the plaster on and that is paintable . I think it is called annaglipta (sp?) . Or line the room in a wood cabin siding and then white wash it . Then you could hang a mirror and have a row of coat hooks and maybe a shelf under the mirror . and a washable area rug or matt

Oh it is not just the paint coming up it is the plaster that the old owner put over the original plaster ( why I am not sure. I have am going to put a false wall over it. MDF panel. I will apply the paint or wall paper or antique mirrors on that which will be achored into the wall. I was going to do a batten board with it but really like the look of the antique mirror wall on one side.