Sory, but can't find last news about it!
Why BTC/CNY now cheaper than BTC/USD?
it isn't really that cheap. you are converting CNY to USD and using a rather different price for CNY/USD pair that is why there is a difference.
also, there is always going to be some difference between prices of bitcoin in different currencies.
on top of that, as it was mentioned these Chinese exchanges are having some troubles these days (which i think was finished recently) that is why Chinese people are trading elsewhere. if you check the localbitcoins price for example you can see the CNY price for bitcoin is much higher now.