You haven't actually shorted the market, but if prices increase over the next 6 months, you may end up losing money on the tickets you sold. This is why you see airlines hedging, because they are implicitly short.
The same holds true for housing for most people as I explained above. People rarely downsize their homes. Their forward consumption of housing is almost always greater than their current exposure to the housing market. This leaves them implicitly net short.
I hold that still depends on what your alternative investment opportunities are. If you buy the $1M house when you actually want the $2M house, you are still locking in 50% of the cost. Thats a good thing if the alternative investments perform poorly, and a bad thing if the alternatives are better.
Does it matter what you think your cash investment would meet or beat the real-estate appreciation?