The more central banks mess around with global bond markets, themore you have to question how you invest in bonds.

Think safe-haven debt, such as U.S. Treasuries, will provide ahedge against losses on stocks? Not always. Or that central bankersreally have control over borrowing costs? Or that you ought to getpaid to lend money to Germany, Switzerland, France, and Belgium?Nope, on both counts.

The latest market turmoil is underscoring the difficulties ofrelying on conventional wisdom at a time when bond markets aredominated by the trades of Chinese, European, and U.S.policymakers. While stocks globally just underwent a plunge thateliminated US$5 trillion of value in less than two weeks, bondsacted in some surprising ways.

Treasuries, often a haven for investors fleeing riskier assets,actually lost value after China rocked markets by devaluing its currency to stimulategrowth. Longer-term U.S. government Treasuries have declined2.3 percent since Aug. 17, according to Bank of America MerrillLynch index data.

This doesn't make sense from a purely economic standpoint, sincethe prospect of slower growth should make these securities moreattractive, not less. But there's another force at play. China, theworld's second-biggest economy, which has accumulated trillions ofdollars of foreign assets since 2003, is now selling some of thosesecurities, including Treasuries.

“The potential for more China outflows is huge,” Deutsche BankAG strategist George Saravelos wrote in an Aug. 26 report. “Realyields should move higher, inflation expectations lower.”

Meanwhile, the same slowdown in China's economy that spurred thenation to sell Treasuries is also prompting the U.S. Federal Reserve to consider delaying its first interest-ratehike since 2006.

The decision to begin the normalization process at the SeptemberFed meeting “seems less compelling to me than it was a few weeksago,” Federal Reserve Bank of New York President William C. Dudleysaid in an unscheduled statement Wednesday.

That supported stocks, as would be expected. Yet even asderivatives traders were pushing back expectations for when the Fedwould likely raise rates, yields on two-year Treasuries rose.

Over in Europe, logic has been turned on its head, withinvestors receiving negative yields on two-year bonds in a numberof its major economies.

That might make sense if Europe was about to sink into arecession, but the European Central Bank has said it's willing toexpand stimulus efforts to spur growth. That may leave traders withbigger losses than they're pricing in right now.

So if you think you know what's happening next in the bondmarket, these recent moves mean you might want to think again.

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