I just tried to reproduce this problem, but couldn't.
Installed the ubuntu 20.04 daily built image on my Lenovo X1 Carbon 7th sudo apt dist-upgrade reboot and check the pulesaudio version, it is 1:13.99.1-1ubuntu1
Paring a bluetooth headset (Sony WL-1000X), it connected successfully check the gnome-sound-setting: the output device is Headset - WL-1000X the configuration is High Fidelity Playback (A2DP Sink)
Click test Front left and Front right, the sound output to my BT headset choose speaker - Cannon point-LP High Definition...(internal speaker), click test front left and front right,the sound output to internal speaker.
Disconnect the BT headset
plug a usb audio bar (one headphone and one microphone)
the output device is automatically changed to USB Speaker - Audio Adapter (Unitek Y-247A) click the test front left and front right, the sound output to usb headphone manually select internal speaker from gnome-control-center, click front left and front right, the sound output to internal speaker.
So looks like everything worked as expected. Didn't reproduce the problem.
Also added my testing result to pulseaudio/issues/832.
I just tried to reproduce this problem, but couldn't.
Installed the ubuntu 20.04 daily built image on my Lenovo X1 Carbon 7th sudo apt dist-upgrade reboot and check the pulesaudio version, it is 1:13.99.1-1ubuntu1
Paring a bluetooth headset (Sony WL-1000X), it connected successfully check the gnome-sound- setting: the output device is Headset - WL-1000X the configuration is High Fidelity Playback (A2DP Sink)
Click test Front left and Front right, the sound output to my BT headset choose speaker - Cannon point-LP High Definition. ..(internal speaker), click test front left and front right,the sound output to internal speaker.
Disconnect the BT headset
plug a usb audio bar (one headphone and one microphone)
the output device is automatically changed to USB Speaker - Audio Adapter (Unitek Y-247A) click the test front left and front right, the sound output to usb headphone manually select internal speaker from gnome-control- center, click front left and front right, the sound output to internal speaker.
So looks like everything worked as expected. Didn't reproduce the problem.
Also added my testing result to pulseaudio/ issues/ 832.