E' lo stesso mio sistema...
Comunque se il file viene riscritto significa che il network manager viene avviato...

emmedi@debian:~$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address 192.168.0.3
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
emmedi@debian:~$ cat /etc/resolv.conf
nameserver 192.168.0.1