We upgraded our blog from 2.9.2 to 3.1 version. Everything worked fine except that we found a problem with a custom taxonomy related in a custom post type we created.
We experienced problems when special characters (it's a blog in Spanish) were used in the title of the taxonomy.
For example, a custom query had troubles to get the post ID for a post named "La novia de Özil", as well as retrieve the values for the custom fields associated with this post type. Other posts worked fine, but still we see the same problem whenever an accented vowel is used in the name of the taxonomy term (hierarchical).
I don't know if this is a bug or a problem with our database. We experienced the same in both development and production servers.
The charset for both were at UTF-8. We checked also commenting this lines in wp-config.php but the issue remains.
I appreciate any help on finding the problem!
PS. You can see what I mean with the post ID not being read here: http://dev.kienyke.com/ in the FOTO SHOW section, where every title is preceded with the post ID. Check the third thumbnail with missing ID.