Not sure what version it is since the about dialog doesn't report the version but it's the version that comes with debian wheezy. When changing computers the plugin goes back to it's default settings and ignores it's config file. If I logout and log back in again it will return to it's old settins. If I attempt to change the settings it will let me set the options and overwrite the config but will not let me use anything other than the defaukt (us) keyboard layout.
I'm also seeing this behavior with a USB keyboard through a KVM switch. Ubuntu 11.10 i386 xfce4-xkb-plugin 0.5.4.1-1 I can add keyboard layouts and configure the compose key, but when I come back to this computer with the KVM switch, I have only the default keyboard layout and the compose key setting is disabled.
This is likely a duplicate of bug 5637 and should be fixed in the master. Please reopen if it still happens. *** This bug has been marked as a duplicate of bug 5637 ***