[nichtich]

I don't think you understand what he means. If you change RMB to USD then there must be someone changed USD to RMB as your counterparty. The RMB you had never leaves China(unless one day RMB has the status like USD where people use it outside US for things unrelated to US), it's just in some other people's hands now.

[seanmcdirmid]

Yes, I get that. But it isn't that simple...it doesn't have to be "now". The RMB I'm changing to USD today was probably bought 5 years ago (when China had a huge trade surplus and lots of excess dollars on hand). Hence why China has to sell treasuries today to give me my USD. I'm not technically "trading", the RMB is not fully convertible in that sense.

Companies are still trading, earning USD, changing it to RMB. There are still trade surpluses. But it isn't enough to keep the surplus steady, the surplus will now shrink for awhile.