When adding a Group if the parent value is null the Group won't be added to the World, so it's up to you to add it when ready. If parent is undefined it's added to World.

Author: photonstorm

src/core/Group.js

@@ -10,18 +10,20 @@
 * @classdesc A Group is a container for display objects that allows for fast pooling and object recycling. Groups can be nested within other Groups and have their own local transforms.
 * @constructor
 * @param {Phaser.Game} game - A reference to the currently running game.
-* @param {Phaser.Group|Phaser.Sprite} parent - The parent Group, DisplayObject or DisplayObjectContainer that this Group will be added to. If undefined or null it will use game.world.
+* @param {Phaser.Group|Phaser.Sprite|null} parent - The parent Group, DisplayObject or DisplayObjectContainer that this Group will be added to. If undefined it will use game.world. If null it won't be added to anything.
 * @param {string} [name=group] - A name for this Group. Not used internally but useful for debugging.
 * @param {boolean} [addToStage=false] - If set to true this Group will be added directly to the Game.Stage instead of Game.World.
 */
 Phaser.Group = function (game, parent, name, addToStage) {
 
+    if (typeof addToStage === 'undefined') { addToStage = false; }
+
     /**
     * @property {Phaser.Game} game - A reference to the currently running Game.
     */
     this.game = game;
 
-    if (typeof parent === 'undefined' || parent === null)
+    if (typeof parent === 'undefined')
     {
         parent = game.world;
     }
@@ -33,20 +35,16 @@ Phaser.Group = function (game, parent, name, addToStage) {
 
     PIXI.DisplayObjectContainer.call(this);
 
-    if (typeof addToStage === 'undefined' || addToStage === false)
+    if (addToStage)
+    {
+        this.game.stage.addChild(this);
+    }
+    else
     {
         if (parent)
         {
             parent.addChild(this);
         }
-        else
-        {
-            this.game.stage.addChild(this);
-        }
-    }
-    else
-    {
-        this.game.stage.addChild(this);
     }
 
     /**