While I don't have a solution, I can confirm this behavior in Connect. I had an event where everyone recieved 11-20 thank you emails after the event. It would be nice to know why this is happening and how to stop it.
Hello! Has anyone found a solution to this? I find it happening in our Connect as well, and really really need a solution.
I've read that it has something to do with how many times someone logs into the event but I haven't been able to figure it out either and we are having this problem too.