First and foremost, concealment, stealth and all things having to do with hidden have gotten huge rewrites since PHB1.
So let's start with the basics. Concealment from the RC 220:
If an attacker can’t get a good look at a target, the target has concealment: The attacker takes a penalty to melee and ranged attack rolls against that target. The battle might be in an area of dim light, in a chamber filled with smoke or mist, or among terrain features, such as foliage, that get in the way of vision.
Unless otherwise noted, area powers and close powers are not affected by concealment. Such powers often produce explosions or great weapon swings that don’t depend on vision.
...
Degrees of Concealment There are two degrees of concealment.
Partial Concealment (-2 Penalty to Attack Rolls): An attacker takes a -2 penalty to melee and ranged attack rolls against a target that has partial concealment (sometimes simply called "concealment”). The target is in a lightly obscured square or in a heavily obscured square and adjacent to the attacker.
Total Concealment (-5 Penalty to Attack Rolls): An attacker takes a -5 penalty to melee and ranged attack rolls against a target that has total concealment. The attacker can’t see the target: It is invisible, in a totally obscured square, or in a heavily obscured square and not adjacent to the attacker.
So there is no real conflict between being next to your attacker and having partial concealment (what this power grants). There is no issue with concealment and being adjacent. Concealment and hidden are quite different, you don't lose concealment by attacking, you do lose hidden if you attack. NOTE: partial concealment does not allow you to make a stealth check to become hidden, you need Total Concealment for this.
There is no specific/general override here, it's simply the rules working as intended. The power says you have concealment (a -2 to melee and ranged attacks), if you have CA. If you have CA you have concealment. It's that simple.
