Session Cookies Being Deleted Without Being Coded To Do So

Aside from using code to delete a JavaScript session cookie, what can arbitrarily overwrite/delete a JavaScript session cookie?

I ask because I have something that is working flawlessly in development; but as soon as it's moved into a staging area for testing, it stops working.

My initial thought was that there is something causing the browser to think that it's being redirected to another domain, thereby deleting the session. But further testing indicates this is not the case.

Basically put, I have a detail page for clients that contains nine categories; all categories are loaded in an "expanded" state (shows all information for each category) and has a "hide" link next to the header. Click "hide" and the whole category collapses, and the link becomes "expand"; click "expand" and vice-a-versa.

Also on initial page load, the document looks for a session cookie called "vddstatus"; if it does not exist, it creates the session cookie with default values set so that all categories are expanded; if it does exist, it checks the values and adjusts the expanded/hidden status as needed. This way, no matter what page you go to, when you come back to the details page, it remembers the expanded/hidden status of each category.

Like I said, on the development server it works excellently; in the staging environment, the only time it remembers the category statuses is if you click "HIDE ALL"; anything else it apparently deletes the session cookie and generates a new one, set to all categories expanded.