Even though the gnome-control-center panel checks the user name to not allow '-' as the first character in the name, it is probably safe to be using '--' before the user's name when spawning the command line tools to avoid any problem.
So attached patch fixes it
Created attachment 48031 [details] [review]
Patch to add '--' to argument builders
As I already said on irc: patch looks fine to me.
looks like a good robustness fix. thanks.