Scene switches prior to starting the game fail if preloaded items are used in the activating/deactivating callback
It is often desirable for the game to start at some scene, so the main will usually initiate a scene change.
Since the Stage class lets you know what the current scene is, it is also important that this be accurate as it is possible that some code somewhere might need to access the current scene at startup before everything starts.
With the new preload mechanism this causes problems because the Stage will immediately switch the scene if the game loop isn't running, which bypasses the ability of the code to actually start the preload.
If you then access a preload resource (like say a sound) in the activating or deactivating methods, the browser throws a dom error because the element isn't ready yet.
I'm not sure what the best way to fix this is, currently.