On this page, when you try to unfollow a category, the link does not change to say "Follow" nor does the "Followed Tags" list on the left column change to reflect the unfollow as it does with regular tags until the page is refreshed. There is no indication that the unfollow request actually succeeded other than the popup when you click "Unfollow" again that informs you that you cannot unfollow something that you do not already follow. I think I remember seeing a thread title that could have been about this already, but I never opened and read it... so my apologies if this has already been reported.