Bonds are still doing their job this year as investors’ best friends during a downturn: They’re holding up better than stocks, cushioning the blow for balanced investors. High-quality, investment-grade U.S. bonds have returned 0.9 percent through Wednesday, while the Standard & Poor’s 500 index has lost 7.4 percent on worries about the strength of the global economy. The problem is that bonds are not doing as good a job as in past downturns, and the outlook for them is dim. Super-low interest rates mean bonds don’t pay investors much for the bonds they hold or are buying now. And those bonds may fall in price in the coming months and years if interest rates increase as the Federal Reserve, as expected, continues to move short-term rates higher.