Its not a bug, it happens when you try to open something that is only available in a store that is not the one for your account.
If it wasnlt this app, then at some point you viewed an App that was only available in the U.S store and not the Chinese store.
As I said, the only real way to change this back, is to open something in the Chinese store, that only exists in that store. So it forces the store setting back to the Chinese store.
Otherwise, it will try to download the version of the App in the store its set to.
You may also be able to sign out of your account and sign back in and see if that clears it. Settings->iTunes & App Stores->Apple ID.
Sing out, reboot the iPhone, sign back in, and see if that works.