I'm really interested in what you're saying about direct access to the order book, but can you clarify whether you are referring to a one-day time-frame, two or three days or longer term.
For a day-trade I would close a short and the cfd provider would have no need to hedge if they didn't feel they had to. But if myself and a number of clients all held shorts beyond the close not covered by the longs of other clients that would leave the provider itself short on behalf of it's clients total net positions unless it chose to take the opposite view and balance the order book by going long. What you seem to be saying is that if the cfd provider chooses to leave itself short it does not necessarily have to arrange some kind of stock-borrowing, whereas I thought it would have to at some point, maybe same-day or 24 hours but surely not much longer than that. Your knowledge seems to be greater so correct me if I'm way off track.
As for Vodafone itself I'd be unpleasantly surprised if it could be easily short-squeezed by the cfd providers, but then does anybody know what the daily volume attributable to cfds is compaired to actual trade in the underlying, these days?