Music permanently playing from phone speaker once car turned off

I believe this is a previously unasked question. This is a minor issue, I know.

This problem pertains to the Entune Pandora app, which requires that a phone be connected by Bluetooth in order to work. I never turn my phone's Bluetooth off, so my Samsung Galaxy S7 connects automatically whenever I start my car.

I control everything from the car touchscreen. My phone never leaves my pocket. Easy. Simple. Select a Pandora channel on the touchscreen and jam out to my jams...

Arrive at my destination. Turn off my car. Inexplicably, my jams start blasting from my phone speaker, but there's no visible sign of them--no open apps, no play/pause button, no symbol in the notification bar, nothing. I'm forced to turn my car on just to stop the music.

Is there a way to have the music stop when I turn my car off? This seems like common sense functionality--why have music play from my phone if I can't control it from there?

I'm more interested in knowing why this happens, just out of curiosity. I'm not torn up about just tapping the pause button before I turn off my car, but is this a glitch? Why does this happen?