OKCoin has been pretty glitchy recently. Last week, its LTC/CNY orderbook glitched and went down to 0.03 CNY, they later blamed it on a "hidden bug" (?) in the trading engine: https://www.reddit.com/r/Bitcoin/comments/3sb0dx/regarding_okcoin_ltccny_price_error_resuming/ . Alright I guess, par for the course in China...
And now their BTC/USD futures orderbook is showing negative contract values. How this can even happen is unclear, but it may be an indication of backend problems, or just a websocket problem. It may just be a glitch rather than a bigger problem with their system. Either way, it's not very comforting to see your broker showing negative values in the orderbook.
hat-tip: http://www.bitcoinfuturesguide.com/bitcoin-blog/okcoin-futures-orderbook-showing-negative-contract-values