When I close an Incident and add a comment I can see that comment at the bottom of the Incident detail pane (or whatever you call it when you click on an Incident in the list showing all the Incidents) in the Closed Reason section. If I then add another comment to the Incident the title never changes to Last Comment, which may be working as designed, and the Total is incremented to 1 but when I click on the Total: 1 link and I open the details page I cannot see the Closed Comment anywhere when looking at the Comments tab. The Closed Comment is there when looking at Alerts, Bookmarks, or Entities.
Hi. I tested this as well and believe I see what you are experiencing. The comments as to why something is closed are only visible when you select alerts, bookmarks, and entities. When you select comments, the reason for closing the incident is shown but the comments of why is no longer visible. I will put in a request to look into this.