Create a forum.  Define Whole Forum Grade to be "point" with a Maximum grade of, let's say 5.  Also, define Ratings, Scale, Point with a Maximum of 4.  As instructor, make a post.  As student, make a Reply to the instructor's post.

Now, the instructor is going to grade this one post.  There is a Rate dropdown, that when it is dropped down, allows you to pick a value between 0 and 4, as expected, and correct.

Now go to the Whole Forum grading for this student.  The Rate box doesn't drop, and it allows any value, including negative numbers, to be picked.  Try 10.  This is a "bug" because only 0 to 5 should be allowed.  When you go to "Save" the grade, yes, you are told that your grade of 10 is not between 0 and 5. But the Rate button should not allow 10.

Yes, the "style" of the textbox for Whole Forum rating is different, too.  It does not "drop" as it should, which could be part of the problem.

I am attaching a few pictures to show the differences.

I am not sure if this problem has been around since Whole Forum grading was created, but I will tag it as 3.11.4.

Mary Cooch mentioned that this might be related to MDL-69571.

The relevant discussion about this problem can be found in the Moodle.org forum, https://moodle.org/mod/forum/discuss.php?d=429907#p1729978.