looks like a bug to me. I would contact support.
Win despite no mating material?
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In fact, K+R vs K is an elementary endgame. The mating procedure from the final position in the game is as follows:
Urgh, it was my rook.
u are very unfortunate too lose...it must be a draw......since u ran out of time....
If you ran out of time due to a disconnection (on your end, not chess.com's), I'm guessing you took a loss because it was a sort of "punishment" for abandoning the game. This punishment would be apt for someone who is leaving the game early (without resigning) because he's losing. However, in your case, you are winning, so your abandonment was clearly unintentional. Seems very odd.
So I don't know for certain, but the difference may be that you didn't exactly lose on time (which would have been a draw), but you ran out of time because you weren't there, so the server thought that you had ditched the game. That's just a guess; only a staff member can say for sure.
So i'm going to say it's safe to assume it's either a bug, or the computer thought I had abandoned the game. I guess i'll just have to contact support. Does anyone know how I can contact a staff member?
I remember from previous games that if you run out of time and the person you're playing doesn't have mating material, a draw is declared. However, I played a game today, http://www.chess.com/livechess/game.html?id=45394656, and the other person got a win. I ran out of time because my internet cut out for a moment, could this have influenced the win?