Comment 1 for bug 366279

Thank you for taking the time to report this issue and help to improve Ubuntu.

Since you are seeing the visualization, the hotkeys themselves are working normally but the desktop evidently does not have them mapped to the correct mixer. If you look in System->Preferences->Sound, which device do you see selected under 'Default Mixer Tracks', and which tracks if any are selected? If you select a different device, does this fix the problem?