How do I get my volume keys working?

view story

http://askubuntu.com – My laptop's media keys (volume up/down/mute) are detected via xev and showkey. I can go into System Settings > Keyboard > Shortcuts and set the volume controls with the media keys. However when I try to use the keys they do not function properly. I tried setting the keys and rebooting the system but that hasn't worked. Any ideas? System Info: Dell Latitude E6500 Ubuntu 12.04.1 (HowTos)