Book hidden chapters are not shown on WS

Log in as Admin. Create a Course. Enrol a Student in the Course. Enrol a Teacher in the Course. Create a Book activity in the Course. Go to the Book. Create several Chapters in the Book. Set one of the Chapters as hidden. Enable web services (Site administration > Advanced features). Create a tokens for the Student and the Teacher which are enrolled in the Book's course (Site administration > Plugins > Web services > Manage tokens). Call the core_course_get_contents web service as the Student (MOODLEINSTANCE/webservice/rest/server.php?wsfunction=core_course_get_contents&wstoken=XXXX&courseid=COURSEID) through a HTTP client for testing web services (ex. Postman) where: wstoken => the token created for the Student;  courseid => the course id; make sure the returned data does not include the hidden chapter. *make sure "hidden" attribute is present in the returned data for the Book chapter content (it will be part of the content field of the entry for the file with filename equal to "structure") Call the core_course_get_contents web service as the Teacher (MOODLEINSTANCE/webservice/rest/server.php?wsfunction=core_course_get_contents&wstoken=XXXX&courseid=COURSEID) through a HTTP client for testing web services (ex. Postman) where: wstoken => the token created for the Teacher;  courseid => the course id; make sure the returned data does include the hidden chapter. *make sure "ishidden" attribute is present in the returned data for the Book chapter content (it will be part of the content field of the entry for the file with filename equal to "structure")