We live in a 1970 ranch house. The original ceiling was a "popcorn" ceiling which was scraped off and repainted with another type of textured paint years ago by a previous owner. We have painted the ceiling three in the 11 years we lived here for color changes. It's been years since we last painted, but I have recently noticed some paint cracking near the edge of the wall. It runs in a straight line towards the middle of the room, like along the seam of drywall.

There are no moisture issues as far as we know, no water stains or mold and the roof is only 3 years old. Any ideas why the ceiling paint could be starting to crack? I noticed this in a bedroom at the other end of the house as well.