I noticed today, after the upgrade to 1.8.0 that obviously the ajax vote events are incoming multiple times. Screenshot from phpmyadmin:

My guess is that the user clicked multiple times on the thumbs-up which led to multiple incoming events. I also remember that this happened earlier with "best answer selected" events.

We need to disable the button after the press! We can re-enable then after a successful return.

Alternative: Dont allow another ajax request as long as one is in process.