This may be a problem on my side, but could be a forum bug? In alerts, after opening, I have from time to time decided to "stop watching". I think I have it correct. I tick the box at the bottom "more options" and then untick "watch this thread". This doesn't always seem to work (for me). As an experiment, I have just this moment stopped watching a thread. I came back to the site a couple of minutes later, and the thread was ticked again as being watched.