Bug#917868: xfce4-pulseaudio-plugin: Notifications when volume changes causes plugin to temporarily freeze

[Diego Ongaro <ongardie@gmail.com>]

I ran into this same problem when my notifications daemon was not
loading correctly. That was due to #899377 because I had
plasma-workspace installed. It also caused similar stalls with
nm-applet.

Once I had notifications working (and I verified that with
notify-send), I was able to re-enable the "Show notifications when
volume changes" and it worked fine.

Hope this helps someone,
Diego