I'm wondering if it's confusing to users that there's both a "Post a comment" link at the top of comments and responses on the player page as well as a "comment on this learnlet" box at the bottom of the same section. On a heavily commented page, you don't notice it so much but looks confusing on a page with few/no comments.

Also, the "post a comment" box includes a "discard" button while "comment on this learnlet" does not.

As for the "bug" I've noted that if you start writing a comment, and then you run the player in some way, it crashes the comment field making it inoperable. i.e. you can't continue to enter data into the field. You can however, post the comment during and after the player.