Thanks, but I think the problem is not the resolv.conf. The problem is that ISPConfig doesn't write changes in DNS zones on named.conf. The control panel creates the hosts file (pri.*) but it doesn't add new zones to named.conf. I've copied exactly your named.conf (the howto's).
Everything is ok in the monitoring module. I see MyDNS server instead of Bind, is this ok?
Edit: Yeah! problem solved! ISPConfig saves DNS zones on /var/named/chroot/var/named/named.local, so I added the line:
to named.conf, restarted the server and now it works! Thank you falko for your help, now ispconfig seems to be better