If someone is initiating a vote to kick an afk or for any other reason if the last person to vote to kick the person gives the reason of "Trolling" or "Cheating" and the vote goes through than the person will be banned. This also works if the other team is initiating a vote to kick someone; if you select the person they are wanting to kick (using the reason of cheating/trolling) between the second and third person initiating the vote to kick the player than regardless of the option or if the vote is for kicking the person and the vote passes than the player will be banned instead of kicked.
This is a bug within the game and there is no way to fix it besides disabling the option to vote to kick/ban someone with the reason of trolling or cheating.