C'mon guys... look at the charts. the answer is right in front of you.
Its Bitfinex shorts, the attempt at everyone trying to close their position all at once... only way to close your SHORT position is to BUY BTC. The price is even $10 higher on bitfinex than bitstamp (look at bitfinex volume yesterday - 103,859 BTC - vs 44,040 on bitstamp)

Standard stuff, you see this happen from time to time when heavy hitters short a stock only to later feel the pain when the company delivers twice the expected profit and the stock starts going higher. You gotta buy dem shares back timmy.