Daughter.2 got me a boxfull of books for Christmas - she had my Amazon wish list. When I went through the books, I found two copies of one of them, and three copies of another. And it wasn't a mistake by Amazon, that's what the delivery note said too.
So what happened?
I think it's a user interface issue.
Imagine this. You're using a web site, such as Amazon, you're on the page that shows what you want to buy, and you click on the button that says "buy one". Then you carry on to the next item on your shopping list.
But then you go back and have another look at the page where you just made a purchase.
In going back to that page, there's two possibilities. 1) you're looking at the page just before you click the "buy" button and 2) you're looking at the page just after you click the "buy" button. If it's 2), then there's two possibilities, A) you're just looking abd B) in going to that URL, you, in effect, just click the "buy" button again.
The problem comes, of course, with possibility 2B.
I would imagine that some web sites would say, hey, the customer just repeated the transaction, maybe he doesn't really want two of them, I'll just check back with him and make sure that he does. And other web sites wouldn't.
In the case of Amazon, they do check back, sort of. When you finally go to "checkout", you get a list of what you bought before you commit to it, so you can be sure that the list is correct. And if there's two of anything, then you see that there's two (or three, or more).
Of course, when you're buying three dozen books, you might not check that carefully. And I think that's what happened here.
The same thing nearly happened to Ladysolly; she noticed it at checkout. She thought that Amazon must have changed the way their web site works. But I think it's because she's changed from using her desktop computer, running Windows and Firefox for ordering. Now she uses her iPad, using IOS and Safari, and the user interface is sufficiently different so that what you might think was the same action in both, isn't. With Windows/Firefox, you're repeatedly clicking on the back button, or right-clicking on it and choosing the page. With IOS/Safari, you're swiping backwards and forwards. And it's easy for an action to have a different outcome to the one you expect.
This isn't a bug, it's a feature. However you design a user interface, some people will misunderstand what is actually going on. And this is a lot worse, of course, when you change from one UI to another.
So the lesson to take away, is that you should always check at checkout time, that what you're about to commit to buy, is exactly what you wanted.