Some badges are checked infrequently, the criteria for some badges change occasionally and sometimes new badges are added.. Have you ever used up all 30 votes in a day? I am pretty sure the suffrage was recently added or tweaked, since I was also recently awarded it, and I am quite sure that I have used all 30 of my votes many times over the last ~500 days. See this post. http://meta.stackoverflow.com/questions/68024/i-was-just-awarded-the-suffrage-badge-without-proper-cause