This seems like a big problem for market stability. Maintaining a peg to soverign currencies while keeping the BTS market running is just as impossible when large flows of capital move the USD or CNY prices or when large liquidations of BTS drain liquidity. Its a similar situation to a central bank of small country trying to maintain a peg to the USD; when things are calm and business as usual it works but when the markets moves there simply isn't enough liquidity to maintain price parity. Arbitrage can help find the new equlibrium of prices but can't stop the movement of prices as arbitragers also have finite resources and they will look to maximise return by finding the low point to buy and the high point to sell, their incentives are to put the peg under pressure and ultimately break it if they can.