Nope, not a homonym

I found it! The phrase for which I was looking, that is. Sarah Caudwell's The Shortest Way to Hades, a lovely, literary, murder mystery, has several plot points based on textual criticism. For all I know, Ms. Caudwell made this one up because I can't find it in any of the references I have at hand, but here goes:

"I could understand it," she said in the tone of one trying hard to be reasonable, "if I had been dictating. Muriel has been typing for us, after all, for only six months, and cannot be expected to be familiar with technical terms. But how does she manage to do it when she's simply copying from manuscript?"
It was, I explained, an instance of the phenomenon known to students of textual criticism as dictation interne: the copyist, mentally repeating the words of the original, copies them not as he sees thems but as he imagines hearing them -- it is a fruitful source of error.
"Most interesting," said Selena. "Some day, Hilary, you must tell me all about it. Some day, that is, when I don't have a plane to catch and three sets of papers to finish."

From the same book I got "haplography": the accidental omission of letters or lines that should be repeated, such as 'mispell' instead of 'misspell'