Roku (NASDAQ: ROKU) bashers never learn. Short interest on the streaming video pioneer rose to 9.3 million at the end of August, the largest numbers of shares betting against Roku stock since February. It hasn't worked out well for the naysayers. Roku stock has risen more than 20% so far in September. The stock is now a week away from completing its first year on the market, and it's been one of the market's biggest winners.