One important thing I would like to mention is that Bitcoin price December did not cover the range $25000 - $25500.
May be freebitco.in forgot to add the $500 in the range. Can't blame them since there are so many ranges to cover but still if the price of bitcoin is in between $25,000 - $25,500 then all our bets are lost.
Nice catch! I doubt if it's a mistake. I think Freebitco.in intentionally left that range to significantly increase the house edge. In worst case scenario, the minimum house edge for this event is 9.12% (assuming all bets are made at current odds) or 4.56% (assuming odds are uniformly adjusted with increasing bets).
I think it was a mistake. freebitco.in takes a 5% rake on all bets. Meaning if 1btc total is bet on an event, they take .05btc and distribute the remaining .95btc to the winners. So freebitco.in has no preference for which betting option wins an event, they get paid the same amount either way. It would be borderline unethical to take all of the money bet on an event and not pay any of the bettors.
If the price of bitcoin ends up falling in this range, they will probably return everyones bets.