Basically, for newcomers to this thread, bter has messed up fees on withdraw and deposit that are asymmetric and messing with their economics. The result is that we need to adjust the feed. @huafei is correct that the feed is off by as much as 2%, however I can only account for 1.5% economically and suggest a hard fork of the price feed to accomodate this.
Person A deposits btc, gets the 1% bonus, sells to CNY, withdraws at 0.5% loss. Total: +0.5%.
Person B deposits cny, no bonus, buys btc, withdraws at 1% loss. Total: -1%.
This makes the 1.5% discrepancy clear.