In the song lyrics thread we had examples of what someone called "hyper-correction" - which is where someone changes correct grammar into incorrect grammar (the perils of half an education).
An example I can think of that seriously annoyed me was one where I ended up looking like the culprit. I'd uploaded a program to a shareware distribution site, and included a description that tells the user "it comprises x, y and z". Some misguided pedant who controls the product pages took it on himself to change my text to "comprises of".
There's also such a thing as inappropriate correction - where the amendment is strictly speaking correct, but wrong for other reasons. Someone must have told Michael Caine that "a lot of" was grammatically incorrect when talking about numbers. So he titled his autobiograpy Not Many People Know That. I saw it in the library and nearly yelled out loud (and some pedant better not ask how you could yell in silence). If he couldn't bring himself to use the original form that has passed into legend - "not a lot of people know that" - then he should have thought up another title. The way it is, that correction is as ridiculous as putting a top-hat on a tramp.
Probably the worst example of inappropriate correction I know of is where Kingsley Amis used the title of a song as the title of one of his novels, but made a one-word amendment so pedantic that no one but an English professor would see the point of it - The Folks that Live on the Hill. Why he changed "who" into "that" is something you would only know if you know the difference between a defining and a non-defining clause. (I'll explain, but only if you insist.) At any rate, it's ridiculous.
There are also examples of inappropriate correction where the correctness is not grammatical, but political:
"She is a mistress of the art of..." (Radio 4 book review)
"One person's meat is another person's poison" (also Radio 4, I think)