This applies to tracks you can not mute without setting volume to 0. To reproduce: 1) Set volume to 100% 2) middle-click to mute 3) middle-click again to unmute Result: Panel item shows 100% volume. But real volume is 0%. Correct behavior: Should show real volume (no matter what it is).
Is this still an issue with version 4.9.0? If so please enable the runtime debugging mode as follows: xfce4-panel -q export PANEL_DEBUG=xfce4-mixer-plugin xfce4-panel and attach the output here.
I don't know, but it is an issue with version 4.8.0. I can see in http://git.xfce.org/apps/xfce4-mixer/log/ that there have been a lot of changes done for the mixer for version 4.9.0. http://git.xfce.org/apps/xfce4-mixer/commit/?id=47d1cee0825f316b24ee826c5c2f1d6cd53b465d looks promising in order to work around this, since it is supposed to disable mute/unmute function for such mixer tracks in user interface. I wish I was able to install and test it in Xubuntu 12.04, which has Xfce 4.8 and gstreamer 0.10.36. If someone could send me instructions on how to do it, I could test.