Recently my wife and I remodeled a few rooms in our home. This room had some minor drywall "cracking" between two floor heating vents and windows. I applied some drywall mud, sanded it down, primed it and painted it and the cracking (pictured below) seems to have come back with vengeance. This is the only room in the house where this happens. What do you guys think is causing this? Heat from the duct mixing with the cool being let in through the window? Moisture (I hope not)?
Looks like moisture problems, too much heat, or as the above poster stated the paint isn't bonding properly to the surface beneath it. I'd scrap it all off, clean it with TSP, perhaps paint it with an oil based stainblocker (for sealing the surface), repair it with regular drywall compound, prime it, then paint it. Should be good after that.