Problem with books...

When a user has permission to create book pages, and if the book page type is allowed for multiple taxonomies, and if the user has access to create content in some taxonomies and not others, they should not be allowed to add a book page to books whose existing taxonomy is of a type they don't have access to.

Unfortunately, this is not the case. If a user has access to _any_ taxonomy that can create book pages, then the "parent" menu for the book entry still includes all books on the site, including those that they should be restricted from creating content for.

I'm not really sure if there even is a way to work around this.