As far as I could tell it's like PJF said. You used to be able to get the vote button after leaving a comment cause the refresh link was to the gallery, not the Hot20 like striving said only automatic. or, The &Hot=Y tag is added to the link in from the Hot20, this tag turns off the vote button. When you comment the page reloads without the tag. Apparently, to prevent people from only viewing and voting within the Hot20, this 'glitch' has been fixed.