Opendoor (OPEN) has surged nearly 1,000% since July, but Martin Shkreli called it an "obvious short." EMJ Capital's Eric Jackson, who fueled the rally, is pushing for board changes, including the return of co-founder Keith Rabois. A Stocktwits poll showed 63% of traders still long, despite 21% short interest and a 9% dip Monday. Shares remain up 277% YTD.