Question : Computers are not updating DNS info upon connection

I have Mac's and PC's on my network and both types (but not all of either) are exhibiting the same behavior ever since we changed our Sonicwall to a new TZ190.  That behavior is that DNS doesn't seem to be updating upon initial connection.  Like so:

I have on our internal network a server named: terminal.domain.com
Our website is hosted by NetSol and for that domain I have an A record for terminal.domain.com that points to our external IP for outside RDP access.

From outside Terminal.domain.com resolves to our external IP.  If you bring a computer such as my Macbook Pro into to the office after being on an external (home) connection and try to connect to Terminal.domain.com (which is the internal name of the server) it continues to resolve to the outside IP.  UNTIL, I unplug the cable again, wait a few seconds and then connect it again, at which time it resolves properly to the internal IP.  

I can recreate this behavior on serveral Mac's and PC's on the network.

The Sonicwall's DNS configuration for my primary DHCP Zone is as follows:

Pri DNS: Pri Internal DNS Server
Sec DNS: Sec Internal DNS Server
Alt DNS: Qwest External DNS Server

Ok, so ideas?

Answer : Computers are not updating DNS info upon connection

External DNS should not be referenced in the DHCP configuration.  External DNS servers should only be setup as forwarders on the internal DNS servers.