I have a custom taxonomy on my blog called "movie."
When I assign a post the term "Star Wars" in both the tags and the movies taxonomy, and then publish, both the tag and the movie are given the slug "star-wars". No problem.
BUT, when a post is already published with the tag "Iron Man", and I try to then give it the movie term "Iron Man", the slug of the movie defaults to "iron-man-2", and is impossible to change to "iron-man" because the tag already uses that slug.
If tags and custom taxonomies weren't allowed to have the same slug, I'd just have to accept that, I guess. But they can -- I have plenty of tags and movies with the same slug as illustrated by the first example. So why won't it work in the second example?