Last modified: 2012-09-27 01:10:55 UTC
After clicking the AJAX-ified watch/unwatch tab link, a box is supposed to come up at the top of the page with a brief explanation of what just happened, where to find your watchlist, and how to get the page back off (or on) it. This message doesn't seem to be showing up currently under Vector, which compounds the problem of not being able to see the watch state because the link is hidden.
This was solved in r52849.