I marked a thread as unread, came back later and read it, then noticed the thread stayed unread until I explicitly marked it as Read again. I would expect that feature to be a one time thing, meaning it would automatically be marked as read the first time I read it again after marking it. Is this by design, or a bug?
Not sure if it’s by design or not but I particularly like the “feature”. I use it to keep threads at the top of my unread list that I’m referring to often. 
I just used it for the first time, and agree it is a useful feature. However, it is functionally redundant with watched topics, and is different than any other “Mark as Unread” feature I have ever encountered. Nit picky, for sure…
yes mark as unread keeps things unread
I sorta disagree with this. Watched topics just identifies threads you want to receive email notifications for. I’d say this “feature” is really more like a “Favorite Threads” feature. Agree, it’s sort of an unusual implementation for “Mark as Unread” but it works.
You’ll notice if you hover over it that the tooltip says “Mark as permanently unread until desired.” 
@ Josh - That was a quick fix! 