Got 'Leaver' Penalty even though I was in game.

I queued up in a ranked game. The mid and sup were supposed to switch but they forgot to. The mid laner says "Well I'm gonna leave so yall can remake". I bought items and talked a lot in chat, and even voted for the remake, but got busted with a leaver penalty after the game. I never left base so I assume this was the reason. They need to either make it clear that you will get pegged with a leaver penalty if you don't leave base. Lost a games worth of LP and have lower priority queues now. Really frustrating.

This is the third time I've had to post this. The first time I posted it in Report a Bug. Then I noticed that we are supposed to post LeaverBuster comments in Help and Support. Did that and it was deleted there as well. I just want somebody to tell me why the hell I was slapped with that penalty.