If you look at "/lib/systemd/system/smb.service" you will see that it has minimal specifications as to what it needs.
This lists says "network.target"... unfortunately, that doesn't mean the network can be used. Try adding "NetworkManager-wait-online.service" and see if it does any better.
I was having similar issues in Fedora 17 with Samba not binding to the interfaces at boot time, but working correctly after its services were restarted. I entered 'systemctl enable NetworkManager-wait-online.service' from a root prompt and it fixed the problem. This worked for me before in Fedora 16 with CIFS shares not mounting in /etc/fstab at boot. This thread reminded me to try that option.