xfrun4 doesn't seem to inherit env from the main session that would allow ibus to work. See downstream report at: https://bugzilla.redhat.com/show_bug.cgi?id=555022 Would it be possible to inherit at least these env variables? Or just inherit the entire env?
xfrun inherits any env that's set when dbus-launch is started for the session. Anything added to the env after that won't make it in. If you want something in dbus-daemon's env, you have to get it in there in xinitrc before dbus starts.
*** This bug has been marked as a duplicate of bug 6927 ***