Why did MicroStrategy's stock soar in September? The gains start and end with Bitcoin, but there's more to the story. Shares of MicroStrategy (MSTR 6.38%) gained 27.3% in September, according to data from S&P Global Market Intelligence. The business intelligence software company, known for reinvesting its cash reserves in Bitcoin, generally trended upward along with the leading cryptocurrency. It also accelerated in mid-September, when the company said it would borrow another $700 million to refinance old d ...