Given that, the expectation is not for "the next batch of stories in line", it is for "the current stories ranked from #31-50 inclusive", the way that simply visiting news.ycombinator.com gives you the current stories ranked from #1-30.
Someone prematurely optimized this aspect of Hacker News and it became a bit of a nightmare to use in the pursuit of "correctness" -- this would be good if the notion of "correct" were in fact correct, but it is an ideological purity having nothing to do with the needs of the community at large.
Going to an empty page is simply a bug / broken behaviour.
It may not be a "development" bug, in that the error occurs due to faulty code, but it should certainly be filed as a bug and assigned to someone who addresses user experience issues.
(Which at Google would mean being thrown into a black hole... http://data.whicdn.com/images/25373715/4171_d7e8_thumb.gif)