GNOME Bugzilla – Bug 635547
volume menu interrupts panel menu keynav
Last modified: 2011-08-24 02:28:23 UTC
When a status area menu is popped down, you can use the left/right arrow keys to navigate between the different menus. Until you get to the volume menu, because the first (selectable) item in the volume menu now is the slider itself, and left/right on the slider change the volume rather than navigating to the previous/next menu.
Another reason for making the slider vertical, and replacing the "sound settings" menu item with something shorter (like a single "settings" icon, which one would guess on context is sound settings).
This problem doesn't seem to happen anymore for me.