'csNext' is not returned, it is a parameter in the request

Ohhhh touché, you're absolutely right. I am true moron. Mixing up the request and a response is a rather humiliating new low for me.
Anyway, that makes 100x more sense, and explains why they're doing it: so they can have it saved across all sessions (even though it's not ideal). BTW well done on the monumental effort you put in that whole investigation/write-up.
