Drywall Joint Water Damage
The drywall ceiling in the picture above is obviously
suffering from water damage. The water is leaking onto the drywall and
searching for the easiest path of least resistance and this is normally
where the drywall butts up against the next piece of drywall.
The water will flow through the crack in between the drywall for quite a distance. As it sits there, it will slowly but surely over time, start to weaken the plaster that bonding the two pieces of drywall together.
In the situation above, you're looking at the paper tape that has loosened up and is starting to fall off of the ceiling. If they would have used a fiberglass mesh tape, the damage would look different. Paper tape is a little cheaper to use that fiberglass tape and is used primarily in new home construction.
Keep in mind that this damage would have never happened if the water would have never leaked onto the drywall. It doesn't have anything to do with the installation of the drywall originally.
In the picture above you can see what the drywall looks like before it is taped and finished. These gaps acts like little rivers once the drywall becomes wet.