What is this common misunderstanding called?

Any relation to Tracy Terrell? (Linguist who was my grad advisor)

From The Muppet Movie:

Man at bar, to girlfriend: “Go wash, you’ll get warts”

Kermit: That’s a myth!

Man: Yeah, and she’s my myth!

Kermit: No; myth, myth!

Other woman: Yeth?

I just read this one a few days ago, lucky for you.

I believe this trope (chain of corrections) comes closest.

Edited: And I see the OP hasn’t even been here for a few years, ah well. There it is for anyone else who was wondering.

I’ve heard these called Gilliganisms.

Professor: The boulder instantly disintegrated.
Gilligan: And not only that, it crumbled into a million tiny pieces!

True, but in the film it’s clear the warden mistook it to be a very rude word.

An English gentleman visiting New York City realizes he’s short on dress shirts. He instructs a cabbie, “Please take me to the nearest haberdasher”.

The cabbie answers, “Yes sir, right away”.

A few minutes pass, and the Englishman asks the cabbie, “Are we getting near a haberdashers?”

“Yes sir, real soon”.

A few more minutes, and the Englishman suspects he’s being duped. “Look here man, do you or do you not know where there is a haberdasher?”

The cabbie pulls over and looks the Englishman straight in the eye.

“Look mister”, says the cabbie, “I’m cool. You can be straight with me. Whaddaya after, booze, or women?”