Kyle wrote:
Just bought a foreclosure house, and came to learn that Fannie Mae
hired some drunken chimpanzees to repaint the house before they put it
on the market (my apologies to drunken chimps for insulting them),
gave them some paint and rollers from the dollar store and said "have
at it".

Besides the fact that there were all sorts of runs and drips, and
paint on the stained window trim and stair bannisters, AND the fact
they painted everything the same flat white, I've noticed a problem in
the lower level bathroom (this is a bi-level).

The paint over the tub has started to slough in two spots near the
ceiling, and there is a stain on the ceiling directly over where one
would stand in the shower that looks like a water stain from upstairs
but there's no water or sewage line in the ceiling at that point.

I suspect they painted flat over semi-gloss, which is why the paint is
sloughing. I am planning on re-painting this bathroom with designated
bathroom paint - am I going to run into problems? Will my new, good
paint end up sloughing because of the crappy flat paint underneath?
Any thoughts as to what I should do about what looks like an old water
stain on the ceiling, to ensure that won't show through the new paint?

Flat/Semi-gloss has little to do with your problem. Your new paint will
stick to the existing paint. The problem is the existing paint is not
sticking to whatever's below it (possibly a damp surface or mold or mildew).

I'm sure others can advise an alternative solution to stripping off all the
old paint and properly preparing the surface.

For stains and the like, to keep them from bleeding through your new paint,
you should first cover the area with a sealer like Kilz.

Good luck on your rehab.