I just did one of my regular checks of the site pages I view a lot and have an alert saying I've 4 unread emails, yet when I go to the inbox there is nothing new listed there. Even after checking the inbox the alert stays as it is with only the 8 read emails I'm keeping there for later action.
However, I opened the last email I read from 1 Sept and sent it to the archives, then the alert vanished. Weird behaviour.