No need to panic; this event happend a few days ago, August 1. And no one's certain, but it seems just as likely this is a bug in NTP as it is a deliberate attempt to crash unpatched Linux servers. The way ntpd manages the leap second flag is pretty complex and error prone.
There are over 10 stratum one's that advertise LI=1 as of Wed Aug 1 14:18:51 UTC 2012. Unless this changes another false leap second could occur on August 31, 2012
So yes this was happening on July 31st but may happen as well on August 31.
The fix needs backporting large patchset, yet the next leap second isn't announced. So no need to rush... just wait for a while and do QA. Typical mentality.
Link to thread view of NTP list discussion: http://lists.ntp.org/pipermail/questions/2012-August/thread....