While it's clear rate expectations are slightly higher for 2015, with the Fed expected to raise rates, Goncalves said the market could be positioning for other events as well, such as European Central Bank easing.  "We've got the ECB meeting Jan. 22. The first week of January we get all of the European inflation data. That's going to really set the tone," he said. The market sees a chance that the ECB could announce a quantitative easing-stylebond buying program, but weak inflation data would reinforce that notion.  Read MoreBuying stocks now: The world's easiest trade?  Goncalves said a QE announcement could actually drive yields higher, since the expectations for deflation diminish. The 10-year yield rose after Federal Reserve QE announcements, he said. Bond yields move opposite prices.  Yields have defied expectations all year, with rates at the long end of the curve near the lower end of the 2014 range in recent sessions. The 10-year Wednesday was at 2.26 percent, just below 2.28 percent, a support level traders have been watching.  Read MoreExpect another good year for stocks in 2015: Darst  Goncalves said the market has been building in expectations for a Fed hike in short-term rates. The yield curve has been flattening as yields rose at the shorter end of the curve, particularly the 2-year. Hedging for that trade could be part of the increase in shorts, he said.  "The bond market is increasingly building in a more aggressive Fed," said Adrian Miller, director of fixed income strategy at GMP Securities. He said the Commodities Futures Trading Commission data on Dec. 16 showed net short positions on 10-year futures totaled 258,000 contracts, the second largest ever behind May, 2010 when there were 275,000.
Some investors this holiday season have been busily building what some say could be the biggest short position ever in Treasury futures.