Even though Warren Buffett seems to think the value of UnitedHealth stock is about right, that doesn’t mean investors should ignore the long list of unresolved issues facing the company.

As UnitedHealth Group wrangles with a federal investigation, an executive shuffle and a tanking stock price, a bullish ally has emerged: Warren Buffett. The Eden Prairie-based health giant’s stock price jumped more than 10% before trading opened Friday, following news that Buffet’s Berkshire Hathaway acquired about 5 million shares.