I am working on a site (that I can't give you access to), and have problems with understanding the way the cookie a set. 

Here is the process:

1. Clear cookies and cache in FF
2. Log in, by submitting POST form

Here is the first request-response from FF Developer Tools' "Net" panel.

![enter image description here](https://i.stack.imgur.com/BkO8g.png)

As expected, the browser does not send a cookie for this request, but surprisingly the server does not request a cookie to be set with a "Cookie-Set" header. And even more surprisingly, the very next request *does* send a cookie along. 

Here is the subsequent request-response:

![enter image description here](https://i.stack.imgur.com/te8P0.png)

Where and when was this cookie set? Have I completely misunderstood how cookies are set?