I made some notes about this on the "Tuesday Update" thread but nobody replied to them; I'm not sure if they got lost in the shuffle or if it's just not happening to anyone else. But I decided to make a video demonstrating the problem.
tl;dw: When I try to hide a thread in flattened view, it usually hides the wrong thread. Trying to unhide that thread will, in turn, usually hide another thread, and then I have to go in to Show Hidden to find the one that I didn't want hidden.
(I don't know if there are any rules against posting video of using the forums--I doubt it, now that I've typed that out--but just in case there's concern, this isn't a public video; you need the link to access it.)
I have faith. :)
Was there any kind of update on this? I'm afraid it's still happening.