I'm planning to put crown molding up in my living room, but have an issue with the entrance into my living room. There is nothing separating it from the hallway and I don't want to extend the crown into the hall. I've attached a picture with the entrance I'm referring to. [ATTACH]23940[/ATTACH] The black box is what I want to frame and drywall. Is there anything specific way I should handle this?

In several places in my house I have noticed in the last couple years that where the ceiling drywall is nailed to the joists that the nails are pulling in and creating a about 3/4" diameter shallow divit or indentation. It seems to be getting worse, as in I have noticed more divits over a wider area of the ceiling. The biggest area is on the 1st floor of the house and is under areas that do not have plumbing above. It also happens a good distance from any exterior wall. I have also noticed it in several areas in the second story. A friend of mine that used to be a contractor had an initial thought that the drywall was expanded due to moisture, but did not think that was the case since it was found on the first floor of a two story house and not under plumbing. He also thought that since it was accross a big area and in multiple places, that is was unlikely moisture. What could be causing this? Do I need to worry? When I try to search the internet to find help on this, I find lots of info on "popped" nails. I can not seem to find any info on the opposite problem of nails pulling in. Any info or theories on this problem would be much appreciated.