Music blasts through speakers when alarm goes off

[cydewaze]

So, I'm sitting on the train, on my way home from work, listening to music using headphones. I have an alarm set so I don't miss my stop. When the alarm goes off, I can't hear it because it only uses the external speakers, BUT while the alarm is sounding, the music I'm listening to is also playing through the external speakers along with the alarm, disturbing my fellow commuters.

This never happened on my original Pixel. I'm using the same music player (PowerAmp). How do I make it stop?