Some of our courses are gender-specific. Even though we set up the courses with the gender assigned in the Course Request tab (Departments & Courses > edit class > Course Requests), it does not prevent the boys course from showing in the Available Courses list for girls. We were told by Support that this setting only pertains to scheduling, which seems like a missed opportunity. Since there is nothing to prevent the student from choosing the wrong course and saving their choices, it would be up to our registrar to catch these errors prior to scheduling.
It would make a lot more sense if the student only saw the courses they were eligible to take from the get-go.