Also, I recommend consolidating the listener attachment/removal code to a single function and then call that function as needed. This should be the new code block:

import com.greensock.TweenLite;

function attachListeners() {
this.right_btn.addEventListener(MouseEvent.CLICK, rotateRight);
this.left_btn.addEventListener(MouseEvent.CLICK, rotateLeft);
}

function detachListeners() {
this.right_btn.removeEventListener(MouseEvent.CLICK, rotateRight);
this.left_btn.removeEventListener(MouseEvent.CLICK, rotateLeft);
}

function rotateRight(e:Event) {
detachListeners();
TweenLite.to(picture_mc, 1,
{ rotationY: picture_mc.rotationY – 180,
onComplete: function() { attachListeners(); }
});
}

function rotateLeft(e:Event) {
detachListeners();
TweenLite.to(picture_mc, 1,
{ rotationY: picture_mc.rotationY + 180,
onComplete: function() { attachListeners(); }
});
}

attachListeners();