I'm 100% positive custom games don't count towards the Leaver Penalty. A few things that may be happening here: if you spend an excessive amount of time idle (afk/disconnected/asleep on the keyboard/etc), the exact amount not having been released due to reasons mentioned in my previous post, you'll eventually get hit by the 'leaver buster' system; this is to prevent players from just afking games while alt tabbed, and to punish players who can't manage their time effectively ('but I had dinner!' isn't a valid excuse, know when you're going to eat, or don't eat until after the game). Another possibility is Co-op games; a lot of people don't realize, but they _are_ watched by the leaver buster system, as it's a matched game and one you don't have any say in your teammates (if you're solo queueing).

I believe they removed it, but the 'warning' for leaving custom games was just a product of how 'quitting' a game worked; there wasn't any actual punishment though.

Your leaver level will be lowered after playing games without leaving, though again, the exact mechanics haven't been released.

@Terranos
I didn't see it before so sorry I didn't answer it, but it depends on how long you were disconnected. If you're gone for 90% of the game, it will count as a leave. If you're only gone for 30s, it won't. We don't know the cutoff or whether it's flat/percent/a combination of the two, but we do know that there's a point where you no longer get marked for leaving, but it still counts it towards an 'idle/afk' total that will add up (slower than leaves) to result in a penalty as well.

@Skelbono
Win rate has no affect on whether or not you'll be punished.
Also, it's a bit more strict towards new players, partially to ensure that players don't just keep making new accounts to troll/leave on, and partially to get it through new players' heads that leaving is bad.

Playing dominion is good if you only have 20 or 30 minutes to play.

I left a game this morning. Yeah bad me. It's been 2 weeks since I left one so my record isn't bad but still I was annoyed I had to leave that one game.

I find the best times to play are in the evening when all your chores and things are done. when the kids are settled if you are a parent. I was silly to start a game when I knew i had to go out. but now I've learnt my lesson.