TL;DR: go the the edit post screen, clear the Post permalink/slug (found immediately below the Post Title field) by clicking “Edit”, and then deleting the existing text, and save.
So, what’s happening here:
On the site where the Theme Unit Test data are hosted, the ID of the post in question is 14. When you import the data, the ID of that post may or may not be the same.
With posts with no Title, WordPress generates a permalink slug based on the posts’ ID. So in the original site, WordPress generated a permalink slug using the ID “14”. When you import the data, that permalink slug is retained, even though the post’s ID may change. Ergo, you get a broken permalink.
For reference, see this still-open Trac ticket related to numeric post titles:
http://core.trac.wordpress.org/ticket/5305