Do ratings go away after a time?

[hornakapopolis]

I have a user that is telling me that pictures that they have already rated are allowing them to rate them again. Is this possible?

The user is pretty reliable, but my first thought was that (since they vote on a lot of images) they might be closing the window before CPG responded, but they're saying that it's happening a lot.

I found the table that tracks these, but found that the voters' IDs were encrypted. I don't see why it would, but is it that user ID that CPG links to the vote or the IP? It seems a bit silly for it to be the IP, but it would explain this user's problem as they've recently moved.

Along the same lines, why is this information encrypted in the database?