It sounds a little unreasonable though. There are people who own two houses and live in the new one but take a while to sell the old one because one can't always sell a house when one wants to.
I've long thought this unreasonable. There are also people who own one house and let another or even others out - often in the same area for convenience! I have never really got why this is the schools business! How can they effectively make you sell a house!
I understand there will be a (very) few parents who abuse this - and they should understand that they run the risk of losing their place at any point in their childs schooling if they are found not to be living in catchment (if that was the requirement).
Not sure we will ever solve this completely though!