If the player who has enough mating material runs out of time, the game is a draw because the opponent doesn't have a possibility to mate the player so it is a draw.
Draw insufficient Material Bug

oh kevin, just read the chess rules.. or see this video
u'll find that even ivanchuk winning easily, but he choose to grab white last pawn so he will get a draw..
When a player has low time but enough pieces to mate the opponent, and the opponent has only his king, live chess will sometimes reward the opponent with a draw for no aparent reason such as in this game:
http://www.chess.com/livechess/game.html?id=284390149
It has happened to me quite a few times now..