Sooo, I was gone for 7 minutes. Beginner botgame. Someone was at my doorstep so I had to answer. Had a little chat, and I get 10 minute leaverbuster. While an other person, gone for 15 minutes didn't have leaverbuster and randomly left. Just as buggy as 
release. Nice job Rito, Kappa.
Deep Terror Nami1 votesThe first time you are detected as a leaver you don't get a penalty, but a warning. After that you get 5 minute low priority queues, and it stacks an additional 5 after that. If someone else left for 15 minutes and didn't get LPQ while you got a 10 min, it's because you leave more often than they do.
CyclopsNode1 votesOh, lol. This is only 3rd time leaving. And it wasn't even for long.
Deep Terror Nami1 votesYou can read more info here; https://support.riotgames.com/hc/en-us/articles/201752714-LeaverBuster-FAQ