if you make a bond type mortgage in Denmark, then you trade your bonds directly in the market. this has some benefits to the say home owners. They can speculate:

When interest rates go up, refinance and sell you previous mortgage for cheap.

When interest rates go down, refinance and reap the lower interest rates for just the refinancing costs (you can always repay this type of mortgage at rate 100).

needless to say, the volatility on the bond markets had been extremely good for Danish home owners.