Hmm... very strange. I was trying to reconstruct the votes from the browsers that didn't include referer links, and I discovered that all of them came from the same IP address, and semi-regular intervals over the course of the day, from 07:54 PST, to 19:54 PST.

Unfortunately, I can't figure out which ones these votes are attached to (possibly due to browser or proxy caches being hit, rather than my server), so for whoever it is in the 192.127.*.* address space, if you want your votes to count, you'll need to re-vote (I've modified the voting script so it no longer requires the referer). Sorry 'bout all that. Rookie web developer mistake.