Comment 63 for bug 1685754

there's nothing gnome-session can do really. it's not involved at all. gnome-terminal requests a service provided by gnome-terminal-server. dbus either activated gnome-terminal-server or farms off the task of activating gnome-terminal-server to systemd. The easy, maybe good enough, solution would be for you to tick the "run a login shell" preference in gnome-terminal or set umask in ~/.bashrc instead.