Nice catch! I doubt if it's a mistake. I think Freebitco.in intentionally left that range to significantly increase the house edge.
If the price closes in that range, all bets will be refunded.
Click
here to read the post already made by TheQuin.
Originally I wanted to place a wager in that $500 sweet spot that isn't covered, so now I've taken the plunge and put a modest wager on each of the next four options above the price descrepancy I spotted a few days ago.