Last year you could argue - we did argue - that, once house prices were out of reach of most of the people who would be first-time buyers if only they could afford it, the great housing boom would stall.
At best it would pause until earnings had caught up.
At worst it would fall off the cliff.
Instead, the pause was in activity rather than prices (except in expensive corners of London where special factors drive these things).
This year house prices have once again been going up faster than other prices, not in double digits now, but relentlessly - by 5.9 per cent according to Nationwide - more than twice any measure of general inflation and well ahead of earnings rising at around four per cent.
Nationwide's economist Fionnuala Earley has tried to make sense of this. Her theme is that many people who would have been first-time buyers in easier times are now renting instead.
Others have gone back to live with their parents - who may eventually chip in a deposit to regain possession of their homes. The effect has been to boost demand for rented places, strengthening the market for buy-to-let landlords. So, although rents have lagged behind house prices, lowering the yield on landlords' investments, this larger pool of tenants should leave fewer and shorter "voids" when the property is un-let between tenancies.
The mortgage lenders have been re-assured by the resilience of the buy-to-let proposition and gradually increased the maximum percentage of the value of a property they will lend to a landlord from 75 per cent to 85 per cent.
Landlords themselves have been encouraged by the failure of house prices to crumble as advertised. Many are not concerned about more modest yields so long as the rent washes the face of the mortgage. They are in it for the rising value of their property, which a lot of them see as a substitute pension fund.
Then, the same rising house prices build up an equity in buy-to-let proper-ties, which their owners can use a security for a deposit on more buy-to-let properties.
So long as house prices go on rising - even in mere single digits - buy-to-let is a self-funding phenomenon.
It also generates demand for its product, by driving house prices beyond the reach of more and more people who might otherwise have been first-buyers.
Well, that is not altogether how it looks at Birmingham Midshires, probably the biggest buy-to-let lender (as well as Wolverhampton's biggest private employer).
There they point out that buy-to-let accounts for only six per cent of Britain's mortgages, not enough to inflate the housing market as a whole, though it may in local hotspots. Birmingham, for instance, is described as the "most transient" city in the UK, where many people do not buy a home because they expect to move on in a few months, or years.
Buy-to-let may not be driving house prices on its own.
But what if interest rates rise enough to spoil the arithmetic? How soon do the landlords turn from buyers into sellers?