Did you use fiberglass mesh on the joints or that old paper tape? I used to use that paper tape and it would often peel off when it got wet from the paint. I no longer use that crap. I use the mesh now and dont have that problem anymore. You might apply a fast drying non-water based paint over the joints before you use your latex paint. Something like the alcohol based KILZ. Or, even try some spray paint, I never tried that, but it may work. The gray auto primer may work and will be an easy color to paint over.
Mark