old post, but in addition to Siri, having your mic set to "automatic" will still result in only one of them having the mic being the faster one to die. I also think that when they are put in at the same time, Apple prefers one side, even when set to automatic. For example, if you have the mic set to automatic, and always put your AirPods in at the same time together, the right one will have the mic. Only if you take the right one out and put it back in will it switch to the left.