BlitzenZeus
is correct.
While the article below does not come out and specifically mention your issue, there is a new feature in Windows 8 that if you have automatic updates on, and you choose to not reboot, it will do so for you after 72 hours.
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www.engadget.com/2011/11 ··· -72-hou/So to avoid that problem, just turn off automatic updates and manually check. Microsoft's patch schedule is always the 2nd Tuesday of the month around 10 AM PST. Of course, out-of-band patches and updates can (and have been) released on other days, so it does not hurt to check a few more times each month. But, these out-of-band patches don't happen that often.
--Brian