Dear Maintainer,

   * What led up to the situation?
Connected an analog headset with 3.5mm plug
Gome recognized it and offered to select how to use it - headphones, headset or
microphone
Selected "Headset"
System menu in the top-right corner shows "Headphones - Built-in Audio" as
active sound output device, headphones also work e.g. for playing music
Initiated a new call in Calls app on a VOIP SIP account.

   * What was the outcome of this action?
During ringing, headphone remains selected.
Upon connection or hangup due to no answer, the active sound output device is
switched to "Speakers - Built-in Audio"
Therefore, if the call connects, the other party can't be heard through the
headphones.

   * What outcome did you expect instead?
Being able to talk to my call partner through my headphone.

   * What exactly did you do (or not do) that was effective (or
     ineffective)?
Switched to a USB headset and it behaved as expected, the bug did not appear.
But I'd prefer my analog headset.