If the user change the weight of the grade item on full view page it doesn't change the visibility. However if you click on Edit icon and change any information about the grade item, it also change the visibility of the category total.
Steps to reproduce the problem.

1. Go to Course > Grades > Setup > Full View.
2. Add a category.
3. Create a new grade item and select the recent created grade category as parent category.
4. Hide the category total using the eye icon.
5. Edit the grade item you've created on this category, change any information and save.
6. Notice the category total is not hidden any more.

The expected behaviour would be preserve the visibility of the grade category total.

The code should check if visibility is changing, but it only checks if not hidden (line 597 of lib/grade/grade_item.php and 1692 of lib/grade/grade_category.php).