According to the Financial Times, the amount bearish bets have increased over the past few months. Short dollar positions have increased from 200,000 to 280,000.
The primary reason is the difference in the way the various central banks are handling the commodity price increases. The ECB looks at total inflation, meaning their position has become more hawkish. The Fed looks at core inflation, meaning their position is now more dovish. From the dollar's perspective, there is also the increase in oil prices, which will slow U.S. growth, thereby making the dollar less attractive as an investment.