On Mar 12 the price of Bitcoin started to crash. After stopping briefly at 5600 the price fell below 3900 on all major fiat exchanges. The magnitude of this movement placed a huge stress on the ability of Bitmex to handle liquidations of losing traders. In theory BitMex will in this situation:
Liquidate a position when the account equity is not enough to cover the loss on the position. If the liquidation price is better than the bankruptcy price, the excess goes into the insurance fund. If the liquidation price is worse, the insurance fund covers the difference. If the insurance fund runs out, the winning trader is auto deleveraged.
This move was different, the move was so sharp that Bitmex chose to leave liquidations hanging. At one point there was 20m in bids and over 100m in pending long liquidations. Any move to fill these liquidations as designed would risk fully wiping out the insurance fund. Bitmex decides to gamble and protect the insurance fund and the site by not filling liquidations. At this point Bitmex needs the price to pump, yet it is held down by these liquidations. The most amazing possible thing to save the site would be a temporary pause to allow spot to pump and orderbooks to fill. Bitmex gets their miracle as an ‘unplanned cloud physical event’ (later re-classified as a 'DDOS attack on the chat box' occurs). It is impossible to know the exact details behind this action. What is known and that Bitmex agrees to: this event was enormously beneficial (possibly saving the entire site), and trivially within the ability of Bitmex to carry out.
Once the site was down the price was able to pump. When the site comes back online, traders who were short are now liquidated based on the mark price (5400) even though the actual orderbooks are trading at (4500). Bitmex is able to create a forced bid (short liquidation) and use this to fill a forced ask (long liquidation) while the insurance fund profits off this entire spread. As the market stabilizes Bitmex continues to send in long liquidations for several hours. The gamble paid off and the insurance fund increases after a catastrophic event, to over 36,000 coins.
What does this mean?
Bitmex will act to preserve itself when market stress arises. The insurance fund will switch from a theoretical backstop to a speculative trading instrument controlled by Bitmex trading in its own interest. I have always considered Bitmex one of the most trustworthy sites, I have never come across a credible report of them stealing or having weak security. This event however demonstrates that their advertised systems are at the whim of what they feel is needed for the site and their insurance fund will exploit traders as needed in extreme situations.
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