A coalition housing crash?
George Osborne is learning the hard way that almost anything a chancellor says about tax can have unintended and potentially serious consequences.
I am not referring to the incipient rebellion on the right of his party about the coalition's commitment to equalise the rate of capital gains tax with income tax - thus, for some people on higher earnings, increasing CGT to 40% or even 50%.
I should point out that this spat is a wonderful microcosm of the new politics: economic liberals, such as David Davies and John Redwood, are attacking a Tory chancellor for proposing to throw out an 18% unified CGT rate, which was introduced by a Labour government only a bit over two years ago (and was criticised at the time for being too hard on entrepreneurs).
Mr Davies and Mr Redwood are, in effect, saying that the then Labour Chancellor, Alistair Darling, was a free-market marvel. And that the great Tory tax-reforming chancellor of the 1980s, Nigel Lawson - whose CGT approach Mr Osborne seems to want to emulate - was wrong-headed.
And, by the way, Labour MPs are today more likely to be with Mr Osborne on the need to increase CGT than with his Tory opponents.
How an election changes everything!
But what I am really interested in is the effect on the housing market.
Because it is the uncertainty about what's going to happen that's doing the real damage.
If Mr Osborne had simply implemented the higher tax rate on the day the coalition said that's what it wanted to do, there would probably have been a one-off hit to house prices - as potential buyers of second homes and buy-to-let properties factored into their investment plans the potential increase in future tax they might pay.
But if the uncertainty persists about when the new higher rate will be introduced, the negative effect on house prices could be much greater.
Because for those sitting on significant capital gains above the tax free rate of £10,100, it becomes rational to flog properties pronto - to take advantage of the 18% rate and avoid a tax rate that looks set for most property investors to rise to more than double that.
In a housing market that is still weak, a wave of panicky sales could push down prices in a significant way.
Perhaps that doesn't matter. Certainly, if you are yet to buy your first home and feel priced out of the market, you'll say hooray if prices fall.
But the Treasury is only too aware of the inextricable link between the health of our big banks and conditions in the housing market.
There is a mechanistic link between falling house prices and rising bank losses - because banks are forced by accounting rules to incur losses when the housing collateral underpinning the mortgages they provide drops in value in a substantial way.
And if banks' profits recovery were to be set back by a housing market slump, that would have an effect on their ability to provide credit - which in turn would be a setback to the more general economic recovery.
Which is simply a way of saying that Mr Osborne presumably won't want the uncertainty about what's happening to CGT to persist longer than is strictly necessary.