Do you remember, like, two weeks ago, when people were talking about how the launch of bitcoin futures at Cboe Global Markets Inc. and CME Group Inc. would allow for efficient short-selling of bitcoin and finally deflate the bubble? Smart hedge-fund money was lining up to bet against bitcoin, the thinking went, but had no convenient way to do it on the actual bitcoin exchanges. The only people trading bitcoin were the true believers, so of course it kept going up, but once it was opened up to normal financial players that would end. "The futures reduce the frictions of going short more than they do of going long, so it’s probably net bearish," said Craig Pirrong. 

Each Fund may provide redemptions in portfolio securities or cash at the Advisor’s discretion. With respect to the Matching and Ultra ProShares Funds, the Index Receipt Agent makes available through the NSCC immediately prior to the opening of business on the Exchange on each day that the Exchange is open for business the portfolio securities that will be applicable (subject to possible amendment or correction) to redemption requests received in proper form (as defined below) on that day (“Fund Securities”). These securities, at times, may not be identical to Deposit Securities which are applicable to a purchase of Creation Units. The Fund may also, in its sole discretion, upon request of a shareholder, provide such redeeming shareholder a portfolio of securities which differs from the exact composition of the Fund Securities but does not differ in NAV.

If anything, the problem seems to start with incredibly lax risk management at this exchange.  According to the OKEX statement, the risk management team 'immediately' contacted the client to reduce the size of the trade - begging the question - how did their risk management system allow the trade to occur in the first place?  On the bright side, something like that should be easy to fix, but it is indicative, potentially of how many simple things are being overlooked in the rush to make money from crypto trading.
!! WARNING !!! Note that on CryptoFacilities each contract is denominated by 1 BTC. So if you bought a fraction of BTC you can NOT perform a perfect hedge of the value. If you round the BTC you bought with start capital down, you will have slight overexposure LONG with the left-over BTC. If you round up and short an extra contract, you will have slight overexposure SHORT.