udev is automatically adding a new ethernet device when you make the clone.This is because the MAC address changes when you clone a VM. To fix this, just edit /etc/udev/rules.d/##-persistent-net.rules and
1) delete the old entry:
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?", ATTR=="00:50:56:AA:AA:AA", ATTR=="1", KERNEL=="eth*", NAME="eth0"
2) change name of new entry:
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR=="00:50:56:BB:BB:BB", ATTR=="1", KERNEL=="eth", NAME="eth1"
to
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?", ATTR=="00:50:56:BB:BB:BB", ATTR=="1", KERNEL=="eth", NAME="eth0"
3) reboot
I tested this on Ubuntu 8.04LTS