Perhaps homeowners were scared by the recent jump in interest rates or by the expectation of higher rates ahead, but something sparked a jump in people applying for a mortgage refinance last week.

Total application volume rose 6.3 percent for the week from the previous week. The Mortgage Bankers Association's seasonally adjusted index shows volume remains 31 percent lower than a year ago, when interest rates were lower.

Refinance volume had been falling after rates moved slightly higher, but refinance applications increased 13 percent last week, even as mortgage rates remained steady. With rates at near-historic lows for so long, even tiny rate moves can spook borrowers.

The average contract interest rate for 30-year fixed-rate mortgages with conforming loan balances of $424,100 or less remained unchanged at 4.22 percent, with points decreasing to 0.31 from 0.40, including the origination fee, for 80 percent loan-to-value-ratio loans.

"Treasury yields were slightly lower last week as testimony from [Fed Chair Janet] Yellen was perceived to be more dovish than expected, and as the market received data signaling weaker inflation and retail sales for June," said MBA economist Joel Kan. "These factors kept the 30-year fixed-contract rate flat over the week."

FHA refinances, often used by borrowers with lower incomes or credit scores, increased almost 21 percent. The level of refinance activity for the week was still lower than the week before the Fourth of July holiday and less than half of what it was one year ago.

"It could just as easily be some seasonal adjustment distortion, loosening of underwriting standards, or nice weather sparking home improvement goals," said Matthew Graham, chief operating officer of Mortgage News Daily.

Mortgage applications to purchase a home, which are far less rate-sensitive week to week, increased 1 percent from a week earlier and were 7 percent higher than the same week a year ago.