resolv and DNS mystery (or misery)

Hello All :P

So the basics came to bite me in the @rse.

Here is my setup:
Server 1
running "named" with IP address x.x.x.4 (dedicated PPP connection)

Server 2
running "named" with IP address x.x.x.3 (DSL connection)

(x.x.x.0 is a non-valid network on the Internet. Our firewall/router takes care of the NAT.)

I have two resolv.conf files that look like this:
For Server 1:
nameserver x.x.x.4
nameserver x.x.x.3

For Server 2:
nameserver x.x.x.3
nameserver x.x.x.4

Both servers have been tested with dig and can do name queries using external DNS servers like a.root-servers.net.

I have two questions:
1.)
I sniffed some packets on Server 1 with ethereal and can see that Server 1 is resolving names using Server 2. (makes sense when you look at resolv.conf). But where does Server 2 look to when trying to resolve names when there is no external DNS server configured in its resolv.conf ? :?:

2.)
When I switch-off Server 2, Server 1 is having problems resolving names. If it also has a working connection to the internet why can it not resolve the query by itself? :?: (If I understand the answer to question 1 I'll probably understand why Server 1 is not working.)

Any help or comments are welcome.
Jano