To earn the Vox Populi badge a user must cast "the maximum 40 votes in a day." I notice that no one has earned this badge.
Recently I used 39 votes in one day. Further attempts to vote gave me the "Daily vote limit reached; vote again in # hours." message. The same thing has happened to me today, only this time I have only used 36 votes. I note that today some of my votes were on comments (rather than questions/answers) and two of my votes today were down votes.
Is there any known reason why I can't use all 40 votes?