AFK in game, reconnexion and LP loss

Hi everyone ! Today, during a ranked, I had a big problem : PC crashed for no reason. I was already stomping my lane, and everyone in my team was doing well, so while I was trying to boot again & to come back, we didn't lose too much. I finally came back after more or less 10 minutes ( from ~ 20 min to ~ 30 min ), with the same stuff as my opponent, and we managed to end quickly because we were far ahead. We won the game. And I lost LP. 18LP. Like a normal loss. Not 3 like a dodge.

Is this a normal thing ? Or a bug ?

I understand that afk lose LP even if their team wins, but here, it was totally unfortunate ( PC crash ) and I tried my best to come back in time ! And I did it ! I was not ragequitting or anything, because I reconnected MINUTES before the end of the game.

So I wanted to know if this a bug, or a normal thing, and if this is a normal thing, why ?

P.-S. : I wasn't reported at the end of the game, I absolutely did not "feed" or flame, so there is no way that is a "punishment" for "toxic behaviour" ( flame + afk -> the afk is not unfortunate and is a RQ/int + afk -> same ... )

EDIT : Do you know if this influences MMR ? Is it increased ( I won the game ), decreased ( I lost LP, so this might be a punishment as well ), or unchanged ? If it is not a bug, is Riot aware that with this system, next time I got a huge bug ( Game crash, PC crash, connexion crash, whatever ) I won't even bother trying to come back, because I'll lose LP anyway, and I'll better enjoy something else over a game where I will have a massive disadvantage due to being afk for several minutes, even if I really could win the game by waiting and playing safe until I'm not longer behind ?