Occasionally your browser caches the flush page. The ?flush=1 tells the server not to cache it, but if your browser has the page cached, it doesn't ever get as far as the server. Try doing F5 and if that fails, Ctrl-F5. Should fix it.
Just expanding a little on jam's last point; if it shows some stuff in blue text at the top of the db/build?flush=1 page and mentions an enum and some page types (Page, Redirector Page, etc) then it IS affecting it, but it's the lack of new fields causing it to look almost the same as if it wasn't changing.
Alternatively, try swapping this into your $db line and see if it outputs anything in green to signify new fields being added: