The filtering in each column is different. In the Subject Area, the filtering is additive (it's an or/union), but if you click anything under subject area in conjunction with any of the other three categories, it becomes an and/joint operation. This isn't clear to the user so I would suggest adding an explanation making it uniform for all columns.
Thanks for reporting this, @sarazhang! I think we're going to be completely redoing tasks, so I'll leave this open to help us keep this in mind.