Sally.....plaster - or masonry for that matter that is referred to as being "hot" means that it has a high PH. This is generally while the plaster/masonry is wet - by the time it cures, the Ph goes down and there is no problem.
"Hot" plaster can cause a "burn" - the alkalinity will react with the binder in paint and cause it to discolor - it almost looks like a burn - hence the term. Generally paint doesn't peel from a burn - just changes color.
Having said that - alkyd/alcohol based products like BIN can be harmed by high Ph. BIN was not the right product for your case.
I would install that new fan IN the bathrooom - and while you are at it - a new piece of drywall installed and primed with a good latex primer and two coats of latex semi-gloss should do the trick.
Sometimes it is easier to drywall over the problem - as long as the ceiling is sound.
As far as paint goes - Glidden Ultra-Hide Gripper is a great primer - and Glidden Evermore/Ultra-Hide/Ralph Lauren Semi-Gloss are all great finish coats. All are available at The Home Depot.