Why does size of temp internet files folder exceed max folder size?

I am making a web page that detects the size of the "Temporary Internet Files" folder as well as the maximum size of that folder according to the registry. The code works fine, 开发者_StackOverflow社区but with a surprising result: the actual size of the folder can exceed the maximum size set in the registry! Why? I thought that Windows or IE was supposed to automatically delete files once it reached that limit... Any explanation would be very helpful!