I am using Xfce4-mixer 4.10 (Version is not listed in the Version Box) on a Lenovo x201 laptop with Pulseaudion. In general it works fine, but when I mute the sound, I am not able to unmute it again with the panel plugin. I have to press the hardware keys in order to get the sound back working
This is probably a dupe of https://bugzilla.xfce.org/show_bug.cgi?id=8583 More importantly, this won't be fixed. Use xfce4-pulseaudio-plugin instead.