Since bug 41573 the item gets on your watchlist when watchdefault is set and you save a change. But the watch indicator of the actual page doesn't change because the page isn't reloaded.
It would be nice to start the watch animation on submitting the change when watchdefault is set and the item is currently not watched.
Set the watch indicator to status watched when the submit was successful and the item is on your watchlist.
Set the watch indicator back to status not watched when the submit failed and the item is not on you watchlist.
Whiteboard: papercut, backlog u=dev c=WikidataRepo p=3