You all probably know this but, when you vote the xp you earn for infection gets taken away when you die, but if your on infection when you vote its the opposite. My suggestion is simple, fix that.
It only gets taken away if you don't have a full level, you have to be on infection to vote as well, and you have to be alive.
When you vote, you receive three levels with the chance of extra. You do not receive any exp. The only way you could lose the levels you receive from voting is when you vote while not on infection, or you vote while you are a zombie.