Hi MSE,
It sounds like you have a finish corner piece and that is the wrong type. They are made to protect There are a couple of different kinds. One has the metal corner bead with paper edges that is mudded into place. The other is an all metal bead with metal edges that must be nailed in prior to compounding. Both go on over the drywall after the drywall is roughed in......MJH

There is also white plastic corner bead that has rows of holes in it. If it's like that it needs to be mudded in.