Changing the audio output device has no effect

My computer has two audio output devices: a HDMI Display with speakers and a USB headset. Both devices appear in the Gnome sound settings menu as output devices.

But the sound always comes out of the speakers, no matter which output device I choose. So selecting “Headphones” from the Output Device drop down does not change anything.

This affects all audio playback on the computer (Test-button in the audio settings dialog, videos, browser, games etc.).

How can I change the audio device? Why do the audio settings not change anything at all?

Please post more information about audio server and sinks (output devices)

pactl list cards; echo; pactl list sinks; echo; pactl info