The specter of the Federal Reserve moving sooner rather than later to raise official interest rates got the blame for last week’s stock- and Bond-market selloff, but the real culprit might lurk elsewhere.

While the short end of the yield curve is the area that is most sensitive to shifting expectations about monetary policy, years of asset purchases have left central banks with burgeoning balance sheets that also give them substantial sway across the yield curve, said Steven Barrow, currency and fixed-income strategist at Standard Bank, in a note on Tuesday.

So while bond investors are naturally very sensitive to comments about policy rates, they “can be just as sensitive to comments about [quantitative easing] or, indeed, any ‘desired’ move in yields from policy makers,” he said.

U.S. Treasurys sold off last week, pushing the yield on the benchmark 10-year note












TMUBMUSD10Y, +4.29%










 above long-term resistance at 1.6% to hit its highest level since the U.K.’s late June vote to leave the European Union. Rate rise fears were also blamed for a sharp stock-market selloff. Yields and bond prices move inversely.

Stocks












SPX, -1.52%










 were under renewed pressure Tuesday as oil futures retreated, while yields extended their advance.

See Delivering Alpha live blog: Paul Singer says dump long-term bonds

And while stocks typically rally when bond yields are on the rise, analysts say a breakdown in that correlation raises concerns about the near-term outlook for equities and other assets typically viewed as risky.

Read: Why stocks and bond yields aren’t moving in tandem

Barrow acknowledges that the world’s major central banks have been fairly mum on what they would like to see bond yields do, but notes that they’re getting more vocal about other things, including concerns that flat yield curves and negative interest rates in Japan and Europe are taking a toll on the banking sector and the outlook for pensions.

That’s even led some European Central Bank members to make sympathetic noises about the plight of banks, he noted. Meanwhile, Japan’s yield curve—the differential between short-dated government debt and longer-dated issues—has steepened sharply.

In fact, while much of the market commentary last week focused on hawkish signals from Federal Reserve policy makers, it was “cracks” in the Japanese government bond market—with the 10-year yield rising above its 200-day moving average—and the U.K. government bond, or gilt, market that was the true driver, argued Neil Staines, head of trading and execution at ECU Group, in a Tuesday note.

Indeed, Barrow noted that’s left the Japanese bond market with a much steeper curve (see chart below).

Steeper yield curves reflect investor suspicions that central bankers will shape policy in an effort to create a bond market situation that’s more sympathetic to banks and savers, Barrow said. But there is a danger, he writes:

In other words, many investors are looking at things the wrong way around. Treasurys didn’t selloff because of pressure at the front end of the U.S. curve












TMUBMUSD02Y, +5.22%










 stemming from fears of a rate increase, “it actually comes at the long end from the sharp rise in overseas yields,” especially Japanese government bonds, he said.

That means if the Fed holds steady next week, U.S. yields could still rise if investors fear the Bank of Japan is losing control of the long end of its bond market and won’t be able to get yields back down, he said.

So while investors will no doubt be focused on the Federal Open Market Committee as it concludes its two-day meeting on Sept. 21, it’s the Bank of Japan policy meeting that concludes the same day that might be much more important.