Comment 8 for bug 782890

Oh. I guess that's not a module any more, because I'm behind the times on my legacy IPv4 network. :)

So, to check if this is the problem, you can temporarily disable IPv6:

sauer@pyro:~$ ip addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
sauer@pyro:~$ sudo sysctl net.ipv6.conf.all.disable_ipv6
net.ipv6.conf.all.disable_ipv6 = 0
sauer@pyro:~$ sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.all.disable_ipv6 = 1
sauer@pyro:~$ ip addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo

Note that the IPv6 translation address pops up on all interfaces when the disable setting is 0, and goes away immediately when the disable setting is set to 1. To make this permanent on 12.04, create a file named /etc/sysctl.conf.d/60-disableipv6.conf and add a line that says net.ipv6.conf.all.disable_ipv6 = 1. I'm partial to running:
sauer@pyro:~$ echo "net.ipv6.conf.all.disable_ipv6 = 1" | sudo tee /etc/sysctl.d/60-disableipv6.conf
net.ipv6.conf.all.disable_ipv6 = 1
The setting in that file will take effect when you reboot or reload the sysctl settings by running "sudo start procps".

This is still a bug in Precise, IMHO. If IPv6 is going to be enabled by default on the systems, then the Ping6 command should be set in backuppc.pl