Grader fails when adding the Comments block

Add a Comments block in the Grader's page (view.php?id=X&rownum=0&useridlistid=Y&action=grading).

Click on the button to rate any activity.

You get a JavaScript error, and the PDF viewer is not loaded.

"container" is not defined. See this line in comment/comment.js:

var container = Y.one('#comment-ctrl-'+this.client_id);