The Second Ginger Grant - S3-E24
Revealing mistake: When "Ginger" (Mary Ann) forgets the words to the song, she asks the maestro, Mr. Howell, to restart the record. Before and after he puts the needle on the beginning, you hear the music, but the turntable isn't moving.
Answer: Bob Denver answered this when he was on a talk show hosted by Pat Sajak. He said they were going to write into an episode where the castaways found all these clothes, but it got too complicated, so he said, they decided, "who cares, it's only a TV show," and forgot about it. So the writers and actors even asked this, they just never bothered to address it.