Comment 24 for bug 1377005

ok. so, i now know what happens, and why adding anything before the ipv6 address "fixes" the problem.
boot happens like this:
 * system boot
 * net-device-added fires network-interface.conf
 * net-device-added runs ifup --allow auto
 * ifup --allow auto reads /etc/network/interfaces *in order*
 * after the *first* stanza is brought up, /etc/network/if-up.d/upstart is invoked
 * /etc/network/if-up.d/upstart finds all interfaces to be up and emits static-network-up
 * /etc/init/failsafe.conf is stopped, freeing procps.conf to start
 * procps.conf runs sysctl on files in /etc/sysctl.d/*.conf
    which includes /etc/sysctl.d/10-ipv6-privacy.conf

ipv6-privacy.conf ends up killing the existing addresses.