Yeah, after many years using this function on my bluetooth headphones, it's time to differentiate. My smartphone now connects to pc, home cinema, car and headphones. I do like to listen automatically to Poweramp in my car and on the headphones, but not on the home cinema or with the pc (and there it just plays over the phone speakers...). For now, I'll have to turn off the feature until this is implemented. I rather start it manually again instead of turning Poweramp off when not wanting it.
Sorry to bother you, but as I was googling around, I ended up here in this topic, because this problem still exists on my S10+. Would there be any progress towards a solution? Maybe I missed it, but the topic doesn't seam to "solved". Hope to hear from you! Got a very recent Chromecast by the way.