Old permalinks sort of not working

It seems that there is some sort of subtle bug in my import script. If there are more than one entry per day, permalinks to the earliest item turn up an empty page. Here’s an example. The entry as such is sort-of-working, as you can see in this date view, but the permalink (and edit/delete links as well) simply turn up empty pages. The problem doesn’t manifest itself with entries created by dasblog, so I think the bug is in my script.