Why is the default sound not playing in the headphones?

Question

linux

Ubuntu 18.04.
After experimenting with installing/uninstalling different DEs other than KDE, a problem arose.
I connect bluetooth headphones, select them through the KDE widget settings "Volume" as the default device, check the box "Automatically switch all running streams when a new output becomes available". But all new audio streams in the Application tab appear with "Integrated Audio" selected instead of headphones, and play accordingly through the laptop's main speaker until I manually switch to headphones.
How to cure? How can I make sure that when headphones are connected, all new (preferably old) streams go through the headphones?

Answer 1

Found a solution? I have the same problem?!