One time, after I installed XFCE and second audiocard, I've noticed that multimedia volume control keys doesn't work, but I can see a little windows in upper right corner of the screen. And this little wondow show me that volume actually changed. But I don't know wolume of what, becouse my speakers was as loud as before regulation or muting the sound with multimedia keys. So, after some googling, I found a solution, run xfce4-settings-editor, choose there mixer menu and copy "sound-card" property value, which actually was my second card, to property "active-card". And then multimedia keys start to working. So the bug is, that when I cange active card in xfce4-mixer, it change only "sound-card" property, but should change "active-card" property too. Anyway I shouldn't change it through xfce4-settings-editor. May be the right decision would be to add a new option "Active sound card" or something like that. By the way, ubuntu 12.04, xfce4-mixer version 4.8.0-2ubuntu1_amd64, if I can belive apt-get. P.S. Many people blame xfce4-volumed package in such bugs, but it's not that package who's screwed)
Closing old bugs.