Chrome 53 implemented the new css-transforms spec, which mandates that object be flattened when opacity is applied to them.
This doesn't make sense, and breaks 3D scenes that use preserve-3d and opacity at the same time.
If you are making a game engine outside of the web, would you make it so you object become flat like paper when you make them transparent? Of course not!! The same should hold true in the web when using CSS3D.
Please Safari, Firefox, and Edge, don't follow the same route as Chrome. Please. This is my plea, coming from someone who's passion is 3D programming.