Here are a couple of children's literature-related ones, for my records and possibly your interest. The first I noticed a couple of years ago, the second just today.
- Kenneth Grahame claimed in a letter to Teddy Roosevelt that The Wind in the Willows was a sex-free zone. Of course, he didn't use that phrase, but wrote that it was "clean of the clash of sex" - an interesting phrase, I think, but one that is now frequently quoted as "clear of the clash of sex". As far as I've been able to discover, this error goes back to Lois Kuznet's book Kenneth Grahame (1987). That at least is the earliest example I've been able to find. So, it's a pre-internet mistake, but one that now crops up there and everywhere else. (Having said that, I've not seen Grahame's original letter - perhaps Kuznets has - and the difference between 'n' and 'r' can be debatable in some hands. It's just possible I'm maligning her here.)
- Now we have C. S. Lewis's dictum from "On Three Ways of Writing for Children" (1952): “I am almost inclined to set it up as a canon that a children's story which is enjoyed only by children is a bad children's story.” Today I saw this rendered in a student essay as “A children's story that can only be enjoyed by children is not a good children's story in the slightest” - which is just horrible. (I don't agree with Lewis as it happens, but still, what a mangling is here!) Google reveals that this version is now rife - it's quoted in 146 sites, and probably by now in books as well.
I don't know what more I can say, but consider this as a warning buoy anchored by a reef, to warn sailors from sweet song of Lorelei Hardy, siren of lazy quotation.