I've tried unwatching this thread: www.mumsnet.com/talk/am_i_being_unreasonable/4542155-partner-miserable-at-a-show
On my I'm Watching list I click on the little dustbin and it asks me if I want to unwatch, which I agree with. Then a little purple message pops up telling me it's unwatched, but the thread is still there on my list!
I've managed to unwatch some other threads since the site change, but I think this is the first one that's been "Withdrawn", so don't know if that's the reason for the difficulty?