" Automatically watch threads that you create or when you reply... "
Is disabled to all users after an import from vB 4.2.1 (at least on my board). I had to activate it to everybody manually. The home made importer was used during the entire process.
It does work for new registered users.
P.S if you go over your username and press "Preferences", you would notice an overlay. However, there is no overlay to any other option(s), shouldn't it be consistent?