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We're heading into the 4th of July weekend with reasons to be cheerful. The jobs report from the Bureau of Labor Statistics came in surprisingly strong. Unemployment is down to 6.1%, the lowest level since before the financial crisis. And employers reported adding 288,000 new jobs, considerably more than the roughly 212,000 economists had forecasted, according to a Reuters survey.

At the same time, the stock market continued it's rally. After the report the Dow climbed past 17,000 for the first time. So the story here -- more jobs, stronger economy, good news for investors -- is clear, right?

Well, actually, that's if you care only about the stock market. The bond market had a different reaction this morning: Yields on Treasuries ticked up, which means that their prices fell. And while most of us consider bonds the ho-hum, steady part of our portfolios, they stand to take a big hit if employment continues to come back more quickly than expected.

The reason? In the upside-down world on bond investing, a really strong and sustained recovery means the Fed is more likely to raise interest rates -- and rising interest rates cause bonds to fall in value. In this case, the potential slide could be worse because bonds gained in value this year as investors bet that the status quo of low interest rates would hold.

Of course, the jobs report wasn't perfect. There are still plenty of signs of economic slack. Wage growth is still slow. And then there's this:

Remember, the unemployment rate only captures people who say they are still looking for work. The graph above shows that the number people either working or trying to work is historically low. That partly reflects demographic changes, but also a large number of people so discouraged in their job searches they've stopped looking. Numbers like these are one reason Janet Yellen and the Fed may continue to hold rates low despite the better numbers.

Still, after a long period of low rates and strong returns for bonds, people who run mutual funds are worried that many investors are unprepared for rising interest rates. Speaking yesterday, before the jobs numbers came out, T. Rowe Price chief economist Alan Levenson noted that the risk of losses on long-maturity bonds is unusually high. "I don't know that retail investors are aware, as they've ridden this bond market down to lower yields, that the duration of their assets and vulnerability to capital losses is extraordinary by historical standards," he said.

How big a loss are we talking about? An exchange-traded fund owning long-maturity bonds has a "duration" of about 14 years, which roughly translates to a 14% capital loss should rates rise a full percentage point. A more typical fund used as a core bond holding, the Vanguard Total Bond Market Fund, has a duration of 5.6, so would face roughly a 5.6% decline in a one-point rate spike.

This doesn't mean investors should be running away from bonds. Rates could stay low for a long time. And compared to stocks, bonds are still likely to be less volatile, especially in the lower-duration bonds you might have in a short- or intermediate-term bond fund. But today's happy job news is reminder that the era of strong bond returns is likely coming to a close.