When you hear Principal Financial Group (NYSE:PFG) you don't immediately think mortgage banking. Principal offers its 13 million customers everything from retirement planning to insurance to investment services, and is a well-known, well-rounded player in personal finance.

But presented with earnings of $0.62 a share -- well above the $0.34 posted the same quarter last year -- you're right to look for performance enhancers. A stock market rally hasn't hurt the investment business, and folks are feeling good again about kicking some coin into their pension plans. But the real driver behind the second-quarter strength hits much closer to home.

For the quarter, Principal reported a record $17.1 billion in mortgage loan orginations. That's nearly double last year's $9 billion. Clearly, historically low borrowing costs and homeowners looking to move or refinance their present homesteads made for a banner quarter for Principal.

But there's a downside. Have you noticed interest rates ticking higher lately? Wall Street missed the ball here. Coming and going. Analysts following Principal were looking for the company to earn $0.59 a share in each of the second and third quarters. They clearly undershot for June, but they're aiming too high for September.

Realized capital losses and a move to expense stock options have the company guiding estimates down to a range of $0.50 to $0.53 per share in the third quarter. One has to figure that a suddenly lukewarm refi market is eating away at those projections.

For now, it seems as if not just home builders like Lennar (NYSE:LEN) and D.R. Horton (NYSE:DHI) and pure mortgage specialists like Countrywide (NYSE:CFC) may be in for a rude awakening in the second half. With apologies to Lisa and Bart, higher rates can be a Principal Skinner too.

Will interest rates come back down or is the party over? Do you feel the urge to check out our Home Center to learn how to lock into the current rates before they tick higher? All this and more -- in the Buying or Selling a Home discussion board. Only on Fool.com.