disable_ipv6 value in /etc/sysctl.conf not set at boot time

(The following seems to impact Raring, which I believe is a regression from Precise where the following setup did successfully disable ipv6).

I have attempted to disable ipv6 by adding a bunch of configuration flags to the bottom of /etc/sysctl.conf:

    # tail -n 4 /etc/sysctl.conf
    net.ipv6.conf.all.disable_ipv6 = 1
    net.ipv6.conf.default.disable_ipv6 = 1
    net.ipv6.conf.lo.disable_ipv6 = 1
    net.ipv6.conf.eth0.disable_ipv6 = 1

However from a fresh reboot ipv6 is *enabled* on eth0. Perhaps this is because it is trying to be set before that interface has come up. But then shouldn't the all interface cover it? We can see the values currently set:

    # for i in /proc/sys/net/ipv6/conf/*/disable_ipv6; do echo -n "$i: " ; cat $i; done
    /proc/sys/net/ipv6/conf/all/disable_ipv6: 1
    /proc/sys/net/ipv6/conf/default/disable_ipv6: 1
    /proc/sys/net/ipv6/conf/eth0/disable_ipv6: 0
    /proc/sys/net/ipv6/conf/lo/disable_ipv6: 1

Starting up procps again does set the configuration to what I would have expected:

    # service procps start
    procps stop/waiting
    # for i in /proc/sys/net/ipv6/conf/*/disable_ipv6; do echo -n "$i: " ; cat $i; done
    /proc/sys/net/ipv6/conf/all/disable_ipv6: 1
    /proc/sys/net/ipv6/conf/default/disable_ipv6: 1
    /proc/sys/net/ipv6/conf/eth0/disable_ipv6: 1
    /proc/sys/net/ipv6/conf/lo/disable_ipv6: 1

How can I disable ipv6 at bootup time?

----

# uname -a
Linux salinas 3.8.0-19-generic #29-Ubuntu SMP Wed Apr 17 18:16:28 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

# lsb_release -rd
Description: Ubuntu 13.04
Release: 13.04

# apt-cache policy procps
procps:
  Installed: 1:3.3.3-2ubuntu5
  Candidate: 1:3.3.3-2ubuntu5
  Version table:
 *** 1:3.3.3-2ubuntu5 0
        500 http://mirror.anl.gov/pub/ubuntu/ raring/main amd64 Packages
        100 /var/lib/dpkg/status