Bug: Unread replies not sticking

The verticle line to the left of the unread posts in the Notification Feed should remain there if the reply has not been read, but if you go to the Notification Feed, don't view any of the replies, and then exit or go to another thread or site, upon returning it no loner is there to indicate unread replies.

For example:

Without clicking on the unread message and returning to the Notification Feed: