Comment 5 for bug 861388

The real problem is how xfce opens the session and any terminal. It might be because it's not stated as a login.
From an Xubuntu system, logging in and launching who results in an empty list.
Switch to a tty (ctrl+alt+f1-6) and log in there, and you'll see the tty session user if you run who again on the xubuntu session.
Also, using xterm instead of xfce4-terminal results in a correct behavior, so it looks like only xfce session and xfce4-terminal are affected by this bug (gnome-shell is also affected by the exact same bug).

I hope it helps.