It is a mess. there is no legal document. However, people are doing this for a while and it goes well. It is unthinkable in US. However, chinese people do follow games even without legal intervention.
The 70 years usage for land is just nothing. No one really care this. The definition of 70 years of right is not even clear. Additionally, it is a national problem for everyone. Taking the lession from sub-prime, if a problem is too big and universe, it is not a problem at all. I used to have this concern too. But sometimes you have to take action with certain risk.