2014 was a decisively flatter year for the Treasury yield curve.  That means that longer-term (7, 10, 30yr) rates were constantly moving lower relative to shorter term rates.  This wasn't simply a factor of longer-term rates moving lower.  Indeed, they weren't always moving lower in 2014, but on the occasions where rates rose, the shorter-term rates (2-3yr) tended to be rising faster. 

Considering the long term outlook for economic output and inflation combined with the prospect for a Fed rate hike, it makes sense for those shorter term yields to suffer while longer-term debt remains less phased.  It also makes sense to see a bit more support for the short end of the curve heading into the end of the year (i.e. 2yr Treasuries were more resilient vs 10yr Treasuries since Dec 17th).  It's not uncommon for firms to favor shorter term debt for year-end balance sheet considerations.

Once 2015 hit, it was game-on for curve flattening--almost as if the flood-gates were reopened.

I'd hesitate to read too much more into it today.  There's a lot of talk out there about oil and stocks, etc.  I think it's way overdone and possibly even a bad way to look at things.  Bonds clearly had their own agenda today, and if anything, it was coincidentally aligned with the agenda in a few other asset classes. 

The biggest move of the day occurred in high volume at 9:51am.  There is no great explanation for that move and no clear correlation with related markets.  The absence of a clearly-identifiable scapegoat is another feather in the cap of the "2015 tradeflows" story.  In other words, the rally paused for the holidays and is simply getting back to business.  Sometimes it's really that simple.

As they're wont to do, MBS mimicked the Treasury move, but in a more conservative stance.  Fannie 3.0s certainly had a great day of gains, but not quite as great as the long end of the Treasury curve.