DNS Conditional Forwarding

Can anyone help me for a DNS problem i am encountering ?

The server is actually windows 2003. It is not a domain controller and configured as a dns with conditional forwarding. My problem is during the first time that a resolution is being made by the dns server, it performs exactly as I have configured it. It forwards resolution to the proper forwarders for a particular domain (i.e. a.com forwarder is x.x.x.x and b.com y.y.y.y). However there is a particular url (w.a.com) that when resolving the second time, it shows a dns request timed out. I've looked at the logs and its reflecting that on the second time of resolution, the w.a.com is being forwarded to an address that was previously cached z.z.z.z ip address which is not included in the forwarders and cannot be included in our forwarders (in the logs it is in the additional section header). Can anyone help me by telling me what is happening in my dns and how can i correct that problem ? Additionally, what is the additonal section in the logs ?

Hope somebody can assist me here.