Just something interesting to note. Last week I muted a user after getting harassing Private Messages from them. I muted them, and 'left' the PM conversation after that so I wouldn't have to deal with it.
About 12 hours later I get a PM from that same user on that same account further harassing me. I clicked on the profile to find that I could not re-mute the user because the 'mute' option was already checked. The timestamp on the PM indicated it was sent many hours after I had already muted the user.
This occurred on Saturday. I figured it'd be best to wait until the weekday to report it, though.
Firefox. No userscripts.