What happened to the personal savings rate in Q4 2012?

Note the huge increase in personal saving in Q4 2012.

I’m not asking why it tanked between Q4 2012 and Q1 2013. The drop simply put it closer to it’s long term trend. I want to know why it spiked so high in Q4 2012. I came across this chart earlier this morning. I looked up “personal savings rate Q4 2012” on Google but found nothing to explain this. It’s a big jump—something like 30 percent. Any ideas?