A ten thousand year ko precipitated a rules crisis in the Nihon Kiin 1928 Fall Tournament, before there were written rules. The players played as members of two teams, East and West. In the following game Segoe Kensaku, then 7 dan, leader of the East team, gave two stones to Takahashi Shigeyuki, then 3 dan.
The ko is on the right side. White cannot fill at because the surrounding White group would be dead. Black could add a stone inside to make atari and then if White captured Black's stones it would leave a rabbity six killing shape.
According to this Igo Club web page, after Segoe said that there was nothing more to the play, but Takahashi folded his arms and looked at the ceiling. Finally Segoe filled a dame () and so did Takahashi ().
Then the players filled the rest of the dame. According to John Fairbairn's Mindzine article, after Black had filled the last dame Segoe laughed and said, "I don't know, what's happened?" (Saate, yowatta na. -- Igo Club page.)
The referee, Iwasa Kei, told Takahashi to take the ko and fill it and then count the game. But then Kubomatsu Katsukiyo on the West team came over and said that there was a problem, that as long as the ko was unresolved the game was not over. (The implication being that, since Black left the ko unresolved, the game was hung, without result.)
This dispute, and the problematic ruling, provided a major impetus to the eventual codification of written Japanese rules in 1949.