Mortgage rates have defied conventional wisdom this past month by holding steady for the fourth week in a row.

Home loan rates usually follow the movement of long-term bonds, particularlythe 10-year U.S. Treasury. When its yield rises, mortgage rates tend to go up as well. The yield on the 10-year bond jumped 10 basis points (a basis point is 0.01 percentage point) from Friday to Wednesday, yet mortgage rates stubbornly refused to budge.

According to data released Thursday by Freddie Mac, the 30-year fixed-rate average slipped to 4.15 percent, with an average 0.5 point. (Points are fees paid to a lender equal to 1 percent of the loan amount.) It was 4.17 percent last week and 3.65 percent a year ago.

The 15-year fixed-rate average slid to 3.35 percent, with an average 0.5 point. It was 3.39 percent last week and 2.95 percent a year ago. The five-year adjustable-rate average fell to 3.18 percent, with an average 0.4 point. It was 3.21 percent last week and 2.85 percent a year ago.

“For the last 46 years, the 30-year mortgage rate has been almost perfectly correlated with the yield on the 10-year Treasury, but not this year,” Sean Becketti, Freddie Mac chief economist, said in a statement. “From Dec. 29, 2016, through today, the 30-year mortgage rate fell 17 basis points to this week’s reading of 4.15 percent. In contrast, the 10-year Treasury yield began and ended the same period at 2.49 percent. While we expect mortgage rates to fall into line with Treasury yields shortly, this just may be a year full of surprises.”

Mortgage rates are not expected to hold fast last much longer., which puts out a weekly mortgage rate trend index, found that more than half of the experts it surveyed think rates will rise in the coming week.

Federal Reserve Chair “Janet Yellen sent mortgage bond[s] into a nosedive Wednesday, causing prices to move lower and mortgage rates higher,” said Elizabeth Rose, branch manager of Movement Mortgage. “With improving economic data and higher inflation, we can expect higher rates.”

Meanwhile, mortgage applications decreased last week, according to the latest data from the Mortgage Bankers Association. The market composite index — a measure of total loan application volume – fell 3.7 percent. The refinance index dropped 3 percent, while the purchase index tumbled 5 percent.

The refinance share of mortgage activity accounted for 46.9 percent of all applications.

“Mortgage applications fell last week as mortgage rates were little changed,” said Michael Fratantoni, MBA’s chief economist. “Purchase activity fell last week on a seasonally adjusted basis, but remains 3 percent above last year’s pace. Overall refinance volume continues to decrease, with the refinance share at its lowest level since June 2009.  With higher fixed rates, more borrowers are turning to ARMs, and the ARM share reached its highest level since October 2015.”