Whenever people surrender, the team shouldn't be able to see how many people have voted for yes and no. This will only give a biased vote. Also if you see 3 to 4 people voting yes already at this stage of the game, you lose all motivation to play any further. So just don't show how many votes there are/were for yes/no, just say "Surrendered has failed" or "Surrender has succeeded".
EDIT: Also make an animation whenever the Surrender window appears. Right now it just looks like a simple windows rectangle Yes/No question window, which people just want to disappear as fast as possible. I think if there's some nice animation to it, people would be more aware that this is actually a serious vote, which literally ends the game if you vote yes.