How do I stop the Music app from opening on my iPhone when I plug in my headphones?

I've got an iPhone 6 running the latest software. I've noticed since a few updates ago that when I plus in my headphones the Music app opens, even when the phone is locked. I find this really irritating, as there are obviously a lot of other reasons I would plug in my headphones other than to use that app. It also opens to the same song each time (first song alphabetically), instead of something more logical like the last song I listened to.

In any case, I have to assume Apple developers wouldn't create this without a way to turn it off - anyone know how?

(This is almost as annoying as the time they assumed everyone wanted a free U2 album in their music library. Please don't make assumptions on my behalf!)