Hi,
I've replaced a previous 3.1-alpha with the latest preview, and now when I use a registerBeforeRender to set the alpha and beta rotation values, it allows you to rotate the camera before the render, and after the rotation is reset.
Now: http://playground.babylonjs.com/#RWSSKV
Then (August 17): http://playground.babylonjs.com/indexstable#RWSSKV
Is it a bug? Thanks.