When I pass the wrong arguments to a method:
dbus-send --print-reply --dest=org.gnome.Shell /org/gnome/Shell
it gives the error
Error org.freedesktop.DBus.Error.UnknownMethod: No such interface
`org.freedesktop.DBus.Properties' on object at path /org/gnome/Shell
This error message makes no sense. For the record, the correct command uses variant:boolean:true instead of boolean:true.
Not a dbus-send bug. If you look at dbus-monitor while doing this, you'll see that the error message and the machine-readable error name come from the Shell - dbus-send just prints it.
This is a bug in either Shell or whatever D-Bus binding it uses. It's detecting the error "I don't have a method org.freedesktop.DBus.Properties.Set with arguments 'sb'" and assuming that that's because it doesn't have the interface at all.
I'm having trouble figuring out which project I should report the bug against. I grepped in the gnome-shell and dbus-glib source code, but neither contained the string "No such interface" (the string "No such" did appear several times in both, but it was always unrelated). Could you please give me a pointer as to which project might contain the bug?