LOST LP when I won the game!?

What in the world? I even got honored by my team mates!? I was gone for literally less than 2 minutes - its a hot summer and my graphics card overheated (probably from running Spotify in the background). Annoying, but not a problem!

While I restarted my computer, my team played safe and two minutes when I when I came back we initated a team fight, dominated the game and took the Nexus! I was so proud of my team mates, I even got honored by one of them!

Now tell me, why I LOSE 17LP for winning the game? No feeding, no toxicity - all that happened was that my computer overheated since its summer and it needed restarting.

Riot, I want my LP reinstated.