Hello, When Volume control is added into the panel and that you restart the X server, the icon related to volume is there but the one relate to volume bar doesn't appears. To make the volume bar appears again, I've to go into Properties and close the window.
Works for me. Could you explain a bit more what happens? The Volume Icon and the Volume Slider are one control, so they should always appear together. Do you mean the volume slider shows volume 0?