Why can't I change values in my cookies?
OK, found the issue I think. The first cookie is set from the homepage. The second was set from a different page.

I looked in the Chrome "cookies" dialog and found out that I had multiple cookies all set with different paths.

setcookie() has a "$path" argument:


  The path on the server in which the cookie will be available on. If set to '/', the cookie will 
  be available within the entire domain. If set to '/foo/', the cookie will only be available
  within the /foo/ directory and all sub-directories such as /foo/bar/ of domain. The default
  value is the current directory that the cookie is being set in.


So in my setcookie() I now do:

setcookie('region[state]', $state, 0, '/');


...and the path gets saved to "/" every time, and I don't end up with duplicate cookies causing confusion.