Wikipedia's article on threefold repetitions gives a story about an incorrect threefold claim by Karpov against Miles:
The clause about the right to capture en passant and the right to castle is a subtle but important one. In a game between grandmasters Anatoly Karpov and Tony Miles (Tilburg 1986), Karpov had less than five minutes remaining on his clock in which to finish a specified number of moves or forfeit the game. He claimed a draw by repetition after checking his scoresheet carefully, whereupon it was pointed out to him that in the first occurrence of position, Black's king had had the right to castle, whereas in the second and third it had not. Tournament rules stipulated that a player be penalized with three minutes of their time for incorrect claims, which left Karpov's flag on the verge of falling. By then, Miles had taken the draw ...
What if, instead of five minutes left, Karpov only had two minutes? Does he instantly lose on making the incorrect claim?