drag and drop bug in flash cs4

Hi i have a little problem in flash cs4 , there are two items with drag and drop event...

code for box1_mc;

on (press) {

            this.startDrag();

}

on (release) {

            this.stopDrag();

            this._x = orig_x;

            this._y = orig_y;

if (eval(this._droptarget) == _level0.box2_mc) {

            this._visible=false;

            }

these codes working for but if i drag and drop my item to stage(!)

thats alwayz invisible, i mean i drag and drop my item to stage or another one , thats alwayz being invisible but i would invisible only if i drop it box2_mc

is that a bug or my fault can you explain me (sorry for english)