Deconstructing Due-On-Sale

[Robert Carpenter]

Imagine a town with only one house and one bank. The bank makes a loan for $250,000 on a house in 2000 at 5% interest. Now by 2006 the house value has risen to $400,000. If the house is sold the bank naturally wants to get back the balance of its original loan, and make a new 5% loan on the house for $400,000.  In this way it can increase its revenue by 60%.  On the other hand say a bank made a $400,000 5% loan in 2006 but today that house has a market value of $250,000.  If the loan were paid off and the bank lent $250,000 on the house at 5% its revenues now decrease by 38%.  The point is the bank has an incentive to call the loan due on sale   while the housing market is rising but has an incentive to keep its  loans in place while the housing market is declining or so it would seem to me. Is this line of reasoning sound economics or pure nonsense?