Fourth Place and Lose LP???

I was playing with a casual ranked TFT game with my friend, and I ended the game at fourth place. After the game ended, my client pulled up and told me that I lost LP for getting fourth place. Has this happened to anyone else, and could this be a bug in the game?

Note: this is my smurf account, and I'm not upset over this. I just wanted to address this so that no one else is having this issue.