It only occurs in that one specific example because of the way the RC circuit is designed; the capacitor has a reactive response 90° out of phase, which creates current on that phase close to being aligned with one of the bulb phases, and close to out-of-alignment with the other. When you reverse phase rotation, that alignment reverses, too, and the other bulb dims/brightens. It's nothing inherent to phase rotation, just an example of how improper phase rotation can mess with a circuit.