Thanks for your reply.
Both interfaces are assigned ips by dhcp:
iface eth1 inet dhcp
iface eth2 inet dhcp
Replacing eth2 with eth0 would lead to an interface that won't get up.
Now, I've moved the VM under another host OS and guess what! eth1 and eth2 are not available anymore. I get eth3 and eth4 instead.
Still no clue (don't consider running "grep "eth1" /**" and looking through the numerous results an option).