The book creator has some caching problems.
Step to reproduce the problem
1 - Enable the book creator (Click on "Create a book" link, then "Start book creator" button)
2 - Nothing seems to be happened. Book creator is not active.
3 - Press ctrl-f5, and the book creator starts working
4 - Disable the book creator (Click on "Disable book creator" link, then "Disable book creator" button)
5 - Nothing seems to be happened, the book creator remains active
6 - Press ctrl-f5, and the book creator deactivated
This problem happens also to other users (not sure if all users), and in all wikis.