I just tried renaming to "media center 20.desktop" and although the laucher still worked, it went back to creating a second icon on the favourites/launcher bar when MediaCenter is running. Also, you'll notice that none of the other *.desktop files in /usr/share/applications/ have spaces in them. So, replaced the spaces with hyphens again, and I'm back where I want to be.
Ah, so this is probably why in Ubuntu/Unity starting MC from the Unity dash causes a second instance to open and not open from the existing icon.
EDIT: Confirmed. Applying the StartupWMClass fix and renaming from mediacenter20.desktop to media-center-20.desktop fixes the second icon issue on Ubuntu/Unity. It's working as it should be now from the launcher! This should fix any GNOME-based icon issues.
Bob, are there mediacenter20 terminal commands for Play/Pause, Stop, Next, Previous? If so it should easily be possible to add shortcuts to the .desktop file for Ubuntu/Unity users! I might even be able to even get MC added to the sound menu like other media players like VLC, allowing the control of playback and volume.
EDIT 2: Okay, I've been successful at adding MC to the sound menu in Ubuntu, however it doesn't work. My guess is MC doesn't use the
MPRIS2 spec which is required to remote control media players that way.