Yep probably not doing AD start samba 4 service with the "/usr/local/samba/sbin/samba -D" command. nothing with smbd.conf.
Samba 4 will start with the upstart script that you'll find at the end of my tutorial in the downloadable file.
these scripts (once the values modified to the ones needed for your environnement) will simply install latest stable version fo samba and configure it for you.
you only need to reboot between the two scripts.