Comment 28 for bug 1020285

Leap seconds are inserted at the end of a given six-month period. You can see that the leap second that was inserted at the end of 30 June 2012 (IERS bulletin C43) results in an update for "1 Jul 2012" in your file. You can then see that the line for "1 Jan 2013", which is not yet enabled (note the "#" at the beginning of the line) would correspond to a leap second inserted at the end of 31 December 2012, which, as IERS bulletin C44 states, will not occur.

You can obtain bulletin C44 at my link above, and more of them are available at http://hpiers.obspm.fr/iers/bul/bulc/?C=M;O=D

Also, Ubuntu 11.04 (Natty) has reached end of life, so I would imagine it's unlikely that this issue will be addressed for that release. https://lists.ubuntu.com/archives/ubuntu-security-announce/2012-October/001882.html