Is it just me?

I have a book blog.  On this blog I say what I think of books that I have read.  On the whole I read fiction, but occasionally I will read a factual book.  When I do there is one thing that annoys me about them, above all else.
What's that I hear you ask?
Simple really, when you take into consideration factual or non fiction books are based on truth/real life/basic facts, and it's the fact that some authors put erroneous information in their book. If your book is intended to be non fiction, get your facts right!
I have recently read a book in which the author meets several unusual people around the British Isles, one of which is a female hermit, living in Yorkshire, but the author starts by talking about the Pendle Witches, which is correct, (also know as the Lancashire Witches,) but goes on to say they were executed at Pendle, which he also moves into Yorkshire. It's very close to the border, but it is still in Lancashire. 
I probably shouldn't have, but I did e-mail him to tell him where the Pendle/Lancashire Witches were executed. 
Just as an additional piece of information, my sister-in-law has researched her husband's side of the family, (my brother's and mine.)   It turns out that there is a link to the Nutter family from the Pendle area.
Does it annoy anyone else when non fiction writers get their facts wrong?