Book revision number not updated on edit chapter content

Test 1: 1 - Locate an existing book resource or create one. 2 - Note down the course module id from the url: /mod/book/view.php?id= [cmid] 3 - Connect to the database and execute the following query: select b.* from mdl_course_modules m inner join mdl_book b on b.id = m.instance where module = 3 and m.id = [cmid] 4 - Note down the value of the column "revision". 5 - Turn editing on and edit the content or the title of any chapter in the book resource. 6 - Save your changes and execute the query in step 3. 7 - The expected result, revision number incremented by one.