[eluser]skunkbad[/eluser]
I've had some very bizarre experiences using CI's Flash Session Data. For instance, I had a javascript resource being called in the head area of my html, and it was pointing to a resource that didn't actually exist, and that was causing the flashdata to disappear. Once I removed the call to the javascript, the flashdata worked fine. I imagine that the 404 error created by the resource that didn't actually exist was using up my stored flashdata... but I'm just guessing.
In your case I think it might be worth considering that CI's flashdata is stored in a cookie, and isn't a true $_SESSION array on the server. We all know that a true $_SESSION is stored on the server, but cookies are stored on the site visitor's browser. Because the controller is never serving up a view, but rather redirecting, then the cookie is never set. You could probably verify this by using an HTTP header tool to look at what is going on.
