To try stopping is a good idea, thanks! But it still starts playing on its own when I wake up Windows.
Shutting down MB before Windows sleeps and then starting it after waking it works of course.
To my thinking, when Windows wakes, it should continue as it was when it went to sleep. Apps shouldn't start running if they weren't running when Windows went to sleep.
Anyway, it's a first-world problem.
Thanks very much for your help, phred.