It is intended. I, too, dislike the manner of creating links as keys into a hash of memory resident continuations for exactly this reason. It's just not a good way to structure things. It can be made to work, obviously, but it's far from an ideal setup.
I believe the smalltalk-based "seaside" server works analogously.
In fairness, it doesn't tend to bother often, most of my ( and presumably most of all ) traffic being directed to the harder links, none of which use the "fnid" keys. The continuations appear to be used for links that are hiding information ( indexes into current ranking, user-ids for flagging, etc ). It just stings when you click something after coming back to a page and it throws it back in your face.
I don't want to come off as a troll or anything, but how do you expect us to deal with all the parens in the language you built this site in? It's like, all parens.
... which is a really terrible way to run something effectively. Basically, it means it'll fail whenever it suddenly needs something predictable but previously unneeded.
I think we just have different expectations. I see HN as a YC-hosted water cooler - nothing more. It's not important to me that it be bug-free or fast or even up all the time. YMMV.
... which will drive away everyone overly impressed by flashy features and/or who like to whine about every little unimportant thing, like a social news site being down briefly, or not being able to see karma scores. Working as intended probably.