I was trying to get a handle on the issue, before you painted over it again. The underlying issue is still moisture. With a home that old, there is a high probability you have no moisture barriers in place. Being in LA this is a significant problem. The brick walls collect moisture from the air , and so does the plaster, even the ceiling. Without getting into any crazy house science explanations, and make your head spin....
I will tell you there is no easy way to do the paint removal with plaster. You need to first check for lead paint. Then start a long and tedious process of scraping.
My advice is to get a professional in there to help you sort out the issues. I wish it where simpler, and I'm sure someone else has their answer. However this is very complex, and needs to be seen up close. Try www.ashi.com
get a home inspector to help understand the issues.
Or try www.buildingscience.com
to make your head spin some more.
The problem with the good paint, may be that it cannot let vapor through it. It collects at plaster and the painted surface(hope that makes sense), then the trapped moisture makes it peel off.
Sorry about the bad news, it's the design of the house to act the way it does but I think you need to know what you "could" be up against.
Good luck and tell us how you make out...and if we can be of further help.