usually, the icons should be installed in /usr/share/icons, and xfce4-mixer have the same dirs. but xfce4-mixer will change it to /usr/share/xfce4-mixer/icons i checked the icons/makefile. but can't figure out where is the problem..
I can confirm this problem at least on Gentoo. There's a downstream bugreport at the Gentoo's bugzilla: http://bugs.gentoo.org/show_bug.cgi?id=271530
This bug is gentoo -specific issue..., please look at the downstream bug and close this as invalid.
i wonder why xfce4-mixer won't install icons to /usr/share/icons/hicolor by default. PS: I am using archlinux
I guess we could install them as custom stock icons. But the way it is done now should also be fine. I'll consider changing it though.