I just did a little experiment. I created a rubric from the assignment page. When I went to delete the rubric (using the trash can icon) the rubric was completely removed from the course (I checked the manage rubric area).

I then created a rubric from the "Manage Rubric" area. I added it to the assignment (same assignment as above). And then I deleted the rubric from the assignment (using the trash can icon). This time when I went back to check the manage rubric area in outcomes, the rubric was still there. 

To me that is really weird behavior. It seems like no matter where I create the rubric, it should stay in the course even if I want to remove it from an assignment. 

I am curious if others have the same experience and I am curious as to why it behaves like this. Or, am I doing something weirdly wrong?

Any thoughts/comments would be appreciated.