Pure idle curiosity. Whenever I have to paginate through a list of sorted items, I just use page numbers. The param seems to be a hash of some kind, which might allow for things like persistent snapshots, but if so, why do the links expire?
The parameter looks up a closure ("fnid" means "function ID") in a hash/dictionary/whatever. When memory runs low, some (all?) of them get pruned. Hence, links expire.
I don't think it's a good architecture.