It seems that many players aren't able to allow the opponent to undo.
I never undo for the world. I think that the blundering play is also in
my own. I never allow me to undo, if it's an accidental click.
Although, I'm not so concerned about that the opponent undoes.
Because I think that it's not good for acquiring skills that I get win by the opponent's mistake. If the opponent undoes, I can get the chance for improving my skills.
A game in KGS is nothing more than one of the normal game, even if it's a ranked game. I don't lose whatever, if I lose the game. I don't have to win the game by whatever means.
It's more important that I improve my skill than that I win a game.
Anyway, what does seem sure is that
the player who undoes can't become strong.