Sounds like your computers are using your ISP DNS to resolve and not your local DNS. I'm not familiar with OpenDNS and how its configured, but generally you have a list of DNS servers you use and then you have a list of DNS servers you can forward DNS requests onto.
I would take a guess that you have your DNS servers listed under the ISP DNS, meaning the computers resolve to the ISP DNS first.
Or you have your main DNS servers being yours and the ISPs, instead of listing the ISP DNS as a Forward (if not resolved locally).
Check your computers to see what their DNS IP address is. If its your local DNS server, check your DNS server to make sure its resolving to itself before it forwards the request off to the ISP DNS.