I'm not sure if anyone understands exactly what is going on with the Chinese market.  At least if we're talking about Shanghai.  Remember a lot of Chinese investors are not allowed to invest outside the country (I believe this is still the case), so all their money pours into the Shanghai exchange.  That means we could be talking about a lot of investors, with very little experience, who could be causing problems.  

Perhaps the large moves to the upside and the downside (compared to the Hang Seng) are due to the odd set of circumstances surrounding the index?  If there is someway to get a measurement of the type of investors who invest in the stocks of a certain index, as well as their country of origin, that might shed some more light on the subject.