I don't have volume OSD at all anymore when I control the volume from the keyboard, and when I did, it wouldn't show up when I configured anything other than PCM to be controlled with the keyboard keys. When I first installed Kubuntu, the keyboard volume controls seemed locked on the PCM channel. The PCM channel doesn't have a mute option for me, in Kmix, and the mute button on the keyboard wouldn't mute anything (although it would show a Mute on screen display). The solution seemed to be select...
Have you tried setting up your global shortcuts by right clicking the specific channel you want the keyboard to control (instead of just the master channel?) I was having a similar problem: The keyboard volume controls were not affecting whatever I chose for Master Volume from kmix. They were stuck on controlling PCM - and the PCM channel can't be muted, according to kmix. So I could select the Front channel to be the master, and the keyboard mute button would work, but the voume up and down wou...