Hmm, for me that works only for some time and then the problem reappears.

I can trigger the issue by listening to the music player with headphones and then receive, e.g., an email which is alerted with a short beep as it should be. Now after stopping listening to music and unplugging the headphones then the notification sounds are again done using the default notification sounds.

So I wonder if this change in notification sounds back and forth (due to the music player being active or not) is now somewhat broken with the pulseaudio package. Instead of changing the notification sounds from the beeps back to the customized notification sounds, notification sounds seem to be changed back to the default notification sounds. Can anyone else reproduce this?