When you join a game that is about to finish so you didn't catch any respawn (which is very annoying itself) you get a game-statistic of a random guy that was playing that game counted as yours, so when you get back to the main menu showing your rankstat updated, you get free rank-ups not even playing a game.
Thanks for reporting this. We are aware of this issue at the moment. Do you feel like most of profile rank is due to this? Is it something that spoil the fun for you?
Thank you again and keep me updated, I'd like to have your views on this.