Cisco VPN before NAT

Hi,

I have the following problem, and can't seem to find a solution.

I have 2 Cisco routers, A and B with a VPN connection. Both routers  
have a serial interface pointing to external and an ethernet interface  
(Lets call them A and B) pointing to the inside.

Traffic between subnet A and B is NOT NATed and the VPN works fine.

Now, router B has a second ethernet interface (C), to subnet C.

I added this subnet to the IPSEC ACLS on both routers as I want to  
allow subnet A to access subnet C through the VPN.
The tunnel is up and running with no NAT being done.

However, on router B, access from subnet B to C is NATed:

Interface B
ip nat inside
!
Interface C
ip nat outside
!
ip nat inside source route-map NAT interface C overload
!
route-map NAT permit 10
  match ip address 123
!
access-list 123 permit ip SUBNET_B SUBNET_C