DNS resolution with Vista

I currelty use Vista Entreprise RTM. The DNS resolution do not work
like in XP. We have two AD domain child.parent.com and parent.com. My
vista box is member of parent.com. With XP I was able to corretly
resolve server.child but in vista I need to use
server.child.parent.com, how can I change that behavior? It's a bug or
a new security functionnality.

Thanks