I'm pretty sure this happens when one or more earlier posts are deleted, causing later posts to appear on the page previous to the page they originally appeared on, the latter being where the link continues pointing to until the database is properly updated.
It might just be me but this doesn't really make sense? Your message for example has this link:
https://bt.irlbtc.com/view/5198491.msg52981631#msg52981631Do you mean it has to update with the right number of posts in each page? Since there are two tables in the database (one for posts and one for topics).
I'd hate to see the size of this forum's database...
On a sidenote, I hope the new forum software can better deal with 25k pages and 500k replies, I doubt smf was built for it.