Why is _rotation choppy?

I don’t understand this.
I have a container movieclip with several other movieclips laid out in a big circle inside. If I apply any sort of _rotation code (very slow rotation) it is choppy and bad looking.

BUT!

If I take all of the movieclips inside the container and apply this code to each one (simple orbit script):


onClipEvent(load) {
var radius = 1250;
var degrees = -85;

onEnterFrame = function (){
angle = degrees * (Math.PI/180);
degrees += _parent.deg;
xposition = radius * Math.cos(angle);
yposition = radius * Math.sin(angle);

this._x = xposition + 951.5;
this._y = yposition + 1628.3;
this._rotation = degrees+110;
updateAfterEvent();
}
}

They orbit around a center point just fine and smooth. (P.S. that code is just for one of the movieclips, each of them have different set degrees and rotation values, which makes it hard to change all of them… which is why I’d like to just use a simple _rotation)

Both codes produce the exact same movement (several movieclips orbit around a specific x and y coord, compared to all of the movieclips set on their orbit path and rotating the container). Same speed, same path, same rotation, etc… but when simply rotating the large container mc, it is choppy.

What gives?!
This is really bugging me…