product sold out, could still be ordered

[neuling]

Hello (sorry about my bad english, I did translate the text with Google help)
I have set in my shop (1.7) that products who are not in stock, are also not available.
So far so good. However, I still receive orders for products that are not in stock.
Since the "Purchase" button in the shop is properly disabled (if not in stock), I can only explain it to me, that the customer has already days before put the article in the cart, but the order has just sent later.
Does anyone know more? And if it is so: Where can I adjust that products are in the shopping cart (from previous visits) but now sold out can not be ordered? Thank you for your help.

Kind regars!