Pass the Vegetables, Please - S3-E3
Other mistake: The spot where the coconut Gilligan tosses goes through is rounded, the suddenly squared in the close up. The wall in general is differently colored than the rest of the hut.
Other mistake: On the beginning, the butterfly Beasley calls the Pussycat Swallowtail is yellow. Later it's orange. Also, when Beasley holds the cage with the painted butterfly, you can see the wires making the puppet move.
Topsy-Turvy - S3-E10
Other mistake: At the end, after Mary Ann puts the pie down, and Gilligan drinks the juice, he hits the table, flipping the pie into the skipper's face. First, the Skipper starts to wince when Gilligan hits the table, preparing for the gag. Second, the pie tin defies physics by staying exactly in place on the board after the pie leaves it, and after the board bounces once and settles down. Third, Gilligan dips his finger directly into the cream on the Skipper's face, rather than missing a few times.
Lovey's Secret Admirer - S3-E19
Other mistake: At the end of the episode when Gilligan is using the lie detector he says "I love spinach." The lie detector said it was a lie. But in the episode "Pass the vegetables please" spinach is his favorite vegetable.
The Secret of Gilligan's Island - S3-E25
Other mistake: At the end, the Professor and Skipper walk up on Gilligan, who's busy chiseling a message on a stone. Look carefully, because he's hitting the chisel, but the tip never touches the stone, and the 'E' in 'HOME SWEET HOME' (the message Gilligan is working on) is plainly visible.
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.