that is not a bug, it's a chess rule. at the time your opponent's clock ran out, you didn't have enough material to win against the worst possible play, so you get a draw instead of a win for you.
http://www.chess.com/learn-how-to-play-chess.html#draws
how can i report a bug?
I had only King and my opponent has Rook and Knight and several pawns.
His time finished when I take his Queen and game result was Draw : insufficient material. I had 1 minutes more.
I think this bug came with latest patch update.
How can I report this bug?
best regards