This morning I went to a question where the
edit tags button was hidden, however I went over it with my cursor, though I didn't click it, it became visible. However even when I moved my cursor off it it still stayed there. And it seems to be the case that all questions I now visit on AskUbuntu have it visible all the time which is strange because normally it stops being visible after I move my cursor away from it.
I do not currently have 10k+ on any other sites in the SE network so cannot check whether or not they are affected.
I am running Ubuntu GNOME 16.04 with GNOME 3.20 and Firefox 47.