I have that book too. I guess we'll never know which episode that was. Moltke told the story in relation to stopping the tape - something they very rarely did. She claimed responsibility for one of those rare times under the circumstances you described above. Since the scene was re-taped I assume they got it right the second time around.
Actually, Dr. Lang, I disagree that the scene in question was re-taped.
Her comments are prefaced with a reference to on-air bloopers. She starts by admiting she was responsible for some that resulted in re-taping, then recounts the outrageous story of the two actors mixing up their lines. I didn't get the impression that she was implying that the latter scene was re-taped as well. Further, she says when one of them realized what was happening, "...they just had to plunge on ahead, making no sense whatsoever." I understand this to mean they couldn't do a retake.
Regardless, I could be wrong. I was just wondering if anyone ever noticed a scene where the dialog seemed out of character for two of the actors. My guess is that Grayson H. would have been in that scene.