I accidentally downvoted this answer (mostly due to the fact both arrows are too close together and easily missed on touchscreen devices) and then upvoted it back.
Today I just noticed that this answer is still downvoted by me, as if I hadn't corrected it in the first place. I tried upvoting it again, and after refreshing the page, it shows no effect.
The strangest thing is that when I try to unvote, a box appears saying "You last voted on this answer 11 minutes ago".
I haven't touched this answer since not just 11 minutes ago, but a few hours.
Numbers out of sync
Three hours later, the numbers are still out of sync. My downvote is registered from 19 hours ago in my profile, but the dialog box always reports the frozen amount of "11 minutes ago".
Today (13/01) I was able to unvote the answer, so the glitch is gone. I'm not sure if it's been fixed or if the system just eventually unlocked my vote.
On a side note
What does the -1 mean in my reputation box? Does that mean for every downvote I cast, I lose reputation myself?