I wasn't sure whether to post this in troubleshooting or here.
The issue is this. I installed WordPress in a /wordpress directory and then followed the "Install WordPress files and blog in different directories" instructions. This worked like a charm. The trouble is, it breaks the edit_post_link() functionality, because the path for the "I'm logged in" cookies is still set to /wordpress.
I'd like to see this fixed in upcoming versions, but could anybody give me a quick hack in the meantime? I'm not quite acquainted with the WordPress code just yet.
By the way, great work on the software!