I just received a notification while attempting to upvote a post on the main site that I've reached my daily vote limit. I've not been voting "today" (which I realize is delimited in UTC) specifically/artificially to get the Vox Populi badge, but it is on my radar (I'm a sucker for badges and other electronic equivalents of those old shiny gold star stickers), and when I got the notification about reaching the limit, I checked on the badge status. It's showing I'm at 37/40 votes.
I remember this happening before, I think on ac.SE, and unfortunately I don't have specifics but if my memory is correct it happened around the same time I did manage to get the badge on another site (ELU) (again, not trying to abuse the system or artificially increase my vote counts or badges, just had a long day of procrastination, most of which took place on SE). That time also, I remember receiving the notification about reaching my vote limit but still only had somewhere around 37 votes recorded for the day.
I've noticed votes take a few minutes to be "locked in," i.e. you can undo a vote for 5-10 minutes after voting, so I thought perhaps the system would register the 38th-40th votes after that time interval. But as of now my last vote is 29 minutes ago, I'm still at 37/40 daily votes, am unable to vote more, and don't yet have the badge.
Obviously a super-low priority bug, if it is one at all, but I thought I'd mention it.