Issp And Mx Dns Records

I've discovered that if I do not specify the DNS servers for ISSP I can look up A records, but cannot look up MX (mail server) records. If I do specify the DNS server IP addresses, I can look up the MX records just fine.

Anyone else notice this and/or have a work-around?

In my experience if you use DHCP for IP address assignment it should be unnecessary to specify the IP address of the DNS servers as these are served up during the DHCP process. But this seems not to be the case with ISSP.