Flash as3 Var movieClip duplicates

Having multiple movieclips being able to move around on a grid, once dragging it, it seems to duplicate and the 'original' remains in place. What causes it to duplicate in my code?

import flash.display.MovieClip

[SWF(width = 1300, height = 1000)]

var tileSize: int = 100;
var cols: int = stage.stageWidth / tileSize;
var rows: int = stage.stageHeight / tileSize;
var grid: Sprite = Sprite(addChild(new Sprite()));
grid.graphics.lineStyle(0, 0x000000, 0);
var i: int = 0;
for (i = 1; i < cols; i++) {
    var posX: Number = i * tileSize
    grid.graphics.moveTo(posX, 0);
    grid.graphics.lineTo(posX, stage.stageHeight);
}
for (i = 1; i < rows; i++) {
    var posY: Number = i * tileSize
    grid.graphics.moveTo(0, posY);
    grid.graphics.lineTo(stage.stageWidth, posY);


    var ball: the_ball = new the_ball();
    addChild(ball);
    ball.x = tileSize * 5;
    ball.y = tileSize * 5;
    ball.buttonMode = true;

    ball.addEventListener(MouseEvent.MOUSE_DOWN, onDown);
    function onDown(evt: MouseEvent): void {
        addEventListener(Event.ENTER_FRAME, onRunSnapping);
    }

    function onRunSnapping(evt: Event): void {
        ball.x = Math.round(mouseX / tileSize) * tileSize;
        ball.y = Math.round(mouseY / tileSize) * tileSize;
    }

    stage.addEventListener(MouseEvent.MOUSE_UP, onUp);
    function onUp(evt: MouseEvent): void {
        removeEventListener(Event.ENTER_FRAME, onRunSnapping);
    }
}

It's not duplicating, there are just many movieclips stacked on top of each other. You add a new ball for each row you add on the exact same position.

I dont know how you want the balls to be distributed, but try to replace ball.y = tileSize * 5; with ball.y = posY; to see what im talking about.