Couldn't find a thread about this and didn't see it in the known issues sticky so I figured I should post. There seems to be a bug where people can circumvent a server's star rating cap by joining a friend via the steam friends list. There's been a couple times now that I've seen four and five star players in the a three star server, as well as having a friend who is five stars join my game that was on a three star server. Hopefully this isn't old news.
Just a heads up, you can join a 3 star server with any rating up to 3.99 normally. Also, you do not get kicked from the server if you level past the rating cap. It only checks when you first join the game/lobby. It's not a big deal, I find 5star servers to be easier than 3star servers to win in.