The “flight to safety” into bonds many expected when U.S. stocks slumped last week never took off, making big losers out of prominent fund managers and further confusing investors at a volatile time in the market. Stocks plunged in the second half of August, largely on fears of China’s worsening economy, but U.S. Treasury yields did not see the kind of safety bid that many were expecting and has been typical in times of stock-market stress in the past.