Portals: Add Comment button doesnt work if timeline is not empty

Hi,

After a user creates a case, in the edit-case page, if there is nothing in the timeline, then the user can add a comment no problem, after the comment has been added, however (or if something gets added to the timeline via our support team), the button is no longer responsive and does not work. 

Above is a gif illustrating what we are seeing. At the end clicking the add comment button does nothing.