ActionScript 3.0 :: Pushing Value To Array Via Getter / Setter

I seem to have run into a situation where when I push a value to an array held within a singleton via a getter/setter , Flash seem so access the getter over the setter method. Within my command/controller (I am using RobotLegs)

override public function execute():void {
// various line of code here
//Place screenshot image into an array from model for later reference.
model.unitScreenshots.push(screenShot); // screenshot is just a Bitmap object
}

The getter and setter within my model e.g. robot legs singleton
public function get unitScreenshots():Array {
return _unitScreenshots;
} public function set unitScreenshots(value:Array):void {
_unitScreenshots = value;
}

When I set a break point on both the getter and setter, only the getter method is being called, why? I would think that a push value on the array would trigger the setter, not the getter.