Comment 42 for bug 1685754

(In reply to Reuben Thomas from comment #4)
> I am assuming therefore that my umask having been set, by my .profile, by
> /etc/gdm/Xsession, that the same process will (eventually) start
> gnome-terminal-server (via gnome-terminal), and that therefore the umask I
> set should be inherited (as occurs with xterm).

No, Xsession isn't starting g-t-server. gnome-terminal-server is started by systemd or (on older systems like yours) by the dbus demon, and thus inherits that one's umask (unless they change it before the exec).