Why did my paint peel?
I could see a possibility of the mud not being dry after 24 hours tool seeker & Pete. Plaster, although somewhat porous, gets harder as the years go by, alot like concrete. The mud may dry near the surface yet still be soft underneath. Is the peeling occurring on the fringes of your patches or on the patches themselves, i.e. the actual joint compound? It's possible the mud was not completely dry, you primed over the patches and sealed the moisture in and now it's trying to escape thru the primer film. Just my 2 cents. On the other hand, who knows what the homeowner did with the paint you used. They could have let it freeze and thaw for years in a garage or basement. They could have thinned it down with water, or, it quite possibly is passed it's shelf life. Again, just a theory.