Version: (using KDE 4.4.3) Installed from: Ubuntu Packages I have installed only Jack shared libraries, but system setting show the Jack Audio Connection Kit audio outpute, and, sure, it's doesn't work, because I not insall whole Jack. Maybe change Jack detection mechanism?
I've got a new Kubuntu 10.04 installation with the same problem. The System Settings test in the Multimedia area tells me so. I was investigating because the audio is not working through the browser though audio is working through the OS GUI. Start-up, Shutdown, notification sounds play just fine.
Fixed in KDE 4.5.