[eluser]bigtony[/eluser]
Having uploaded my application to a "live" host, upon testing in IE8 I noticed that certain session functions were being ignored. After a bit of playing around I changed the "sess_match_useragent" value in config.php to FALSE and it solved it (I'm also using database sessions).
It all worked fine when on my development machine, and also fine in Firefox even on the live host, just seems to be IE8.
I'm not suggesting it's a CI problem, but just giving a heads-up in case anyone else comes across a similar problem. Next job is to check in more detail to see just why the user agent value changed...