I have had this happen a few times lately. Its probably because they advertise items that they have purchased at previously at the same price or they dont check prices often or have price feeds from suppliers. As things have gone up by silly amounts you place the order, they get the order and try to place with supplier, its loads more than they have sold it for and they just cancel the order. That said its normally a few hours or the next day thats its cancelled. I have however also had it do it pretty much straight away as well which is weird and i cant see the reasoning behind that unless it is some sort of scam with ebay transactions.